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Veterinary Anatomy 

Histology, Physiology 



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Comparative Anatomy 




COPYRIGHT, 1907 
BY THE AUTHOR 
All Rights Reserved 



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PREFACE. 

Only those who, as students, are compelled to review at the close of the 
graded course, the first and second year studies can appreciate the difficulties 
encountered in wading through the standard textbooks on these subjects. Noticing 
the efforts of our best students toward relief by taking notes of lectures a,nd having 
them printed at a cost far above their actual value, I was induced to assemble in 
one volume the essentials of these allied branches. As this work is not intended to 
supplant any textbook, but only as a convenient reference in reviewing, all unnec- 
essary details and illustrations have been omitted. In anatomy and comparative 
anatomy I have followed Strangeway, Chauveau and Grey. In histology, Bohm, 
Davidoff and Huber; and in physiology, Smith, Paton and Kirk. 

J. HANSON. 



ERRATA. 

Page 5 Line 24 should follow line 3 9. 
28 " 2 for striate, read striae. 
31 " 24 " branchial, read brachial. 
31 " 35 " flexor, read extensor. 
51 " 13 " medium, read median. 



PHYSIOLOGY, OOIVIPAKATIVE ANATOMY 



CHAPTER I. 

ANATOMY OF THE SKELiETON. 

Bone tissue appears to the eye in two forms: 

1. Compact; hard and dense, forming the external shell of all bones and 
the mass of the shaft of long bones. 

2. Cancellated; spongy structure, forming the inner mass of all, except the 
shaft of long bones. 

Bones are classed as long, flat or irregular. 

1. T-iong; acting as pillars of support and levers of motion; in the limbs. 

2. Flat; enclosing cavities and protecting important organs. 

' 3. Irregular, where great strength is required, as the vertebrae, etc. 

Covering: — The periosteum; a tough canvas-like membrane, forms the ex- 
ternal covering of all bones; consisting of an external fibrous layer and an inner 
vascular, bone-forming layer, the osteogenetic membrane. 

Marlving: — Eminences and depressions may be articular or non-articular. 

1. Articular Eminences. 

A head is a rounded prominence separated from the body by a constricted 
part, the neck. 

A condyle is a ovoid prominence. 

A trochlea is a condyle having a pulley-like surface. 

A fa^^et is a small articular surface, may be a depression. 

2. Non-articular eminences. 

A spine is a pointed prominence. 

A tubercle is a small blunt one. 

A tuberosity is a larger blunt one. 

A trochanter is a large, strong prominence. 

A crest is a rough ridge, line or border. 

3. Articular depressions. 

A glenoid cavity is a shallow depression. 
A cotyloid cavity is a deep depression. 

4. Non-articular depressions. 

A foramen, aqueduct, canal or meatus is a depression passing through all 
or part of a bone. 

A notch, fissure, cleft or groove is a depression in the border or surface of 
a bone; two of which in contiguous bones may form a foramen, canal, etc. 

A fossa is a depression, rough for attachment of muscles or ligaments. 

A hiatus is a depression leading to two or more foramina. 

Tlie Skeleton: — 1. Axial; in which we describe the skull, vertebral column, 
sternum and ribs. The skull, as the cranium, or that part enclosing the brain, 
and the remaining bones as the face. 

Cranium: — 1. The occipital; supero-posteriorly is the crest from which the 
mastoid ridge descends on either side; below the crest the tuberosity, a^ depres- 
sion on either side and the foramen magnum below. Externally the condyles, 
stylo-condyloid notches and styloid processes; in the notches the condyloid fora- 
men The basilar process extends forward below the foramen magnum, on fts 
upper surface, the basilar fossa, on the lower surface the basilar fissure; the 
cupola is a depression on the inner surface below the crest. 

2. Parietal, uniting in the median line, has on the inner surface a ridge, the 
crpst, which terminates posteriorly in the ossific tentorium, and in the crest is 
the longitudinal groove. 

3. Frontal; forming the forehead, uniting in the frontal suture; also form- 



VETEKINARY ANATOMY, HISTOIX)GY, 



ing part of the orbital and temporal fossae; the external orbital process extends 
outward to join the zygomatic arch, in its upper border the supraorbital foramen; 
the internal orbital process forms part of the orbital fossa, has a large notch 
for the orbital plate of the sphenoid, above which a depression lodges the lachry- 
mal gland; and a small notch which helps to form the internal orbital foramen. 

4. Temporal. 

(a.) The squamosal portion; projecting upward and backward is the zygo- 
matic spine; projecting forward the zygomatic process; on its under surface the 
glenoid cavity, in front of this the condyle, posterior to it the anterior mastoid 
process in the base of which is the mastoid foramen; on the inner surface is a 
groove which, with a like groove in the parietal, forms the parieto-temporal 
conduit. 

(b.) The petrosal; lodges the essential part of the organ of hearing; on 
the inner surface is the internal auditory meatus, which leads to the aqueduct 
of Fallopius and the internal ear; near it is the aqueduct of the vestibule, a 
narrow slit. The mastoid ridge separates the posterior from the external surface; 
in front of it is the posterior mastoid process; crossing the ridge is the mastoid 
fissure. Externally is the external auditory meatus, below it the hyoid process, 
stylo-mastoid foramen and the mastoid protuberance. Projecting forward the 
styloid process; above which is the styloid foramen and below it the opening 
into the Eustacian tube. 

5. The sphenoid has two center pieces which form the body, and two pairs 
of wings. On each side of the body is the pterygoid process, in the base of which 
is the pterygoid foramen; winding around the base is the Vidian fissure. In 
front of this process is the orbital hiatus and optic foramen; and in the body 
a notch which helps to form the internal orbital foramen. On the upper surface 
of the body is the pituitary fossa, in front of this the olivary process and optic 
hiatus; on each side of this surface two grooves, the inner is the cavernous, the 
outer the sphenoidal, fossa; terminating in the foramen lacerum orbitale and 
rotundum. On each side of the body anteriorly a cavity, the ethmoid fossa. The 
posterior border of the wing bounds the foramen lacerum basis cranii, has an 
inner notch, the carotid, and an outer, the inferior maxillary. 

6. The ethmoid; separated from the nasal fossae by the cribriform plates, 
has a prominence posteriorly the crista galli process and laterally the ethmoid 
cells. 

Tlie Face: — 1. Nasal, the smooth upper part of the inner surface is a gutter 
the superior nasal meatus, below this a ridge to which is attached the superior 
turbinal; the anterior extremities unite to form the nasal peak. 

2. The superior maxilla; on the external surface the maxillary spine, above 
it the infraoirbital foramen; the palatine process forms the floor of the nasal 
fossae and the roof of the mouth; along the outer border of the roof is the 
palatine groove, posteriorly the palatine foramen; externally the molar alveoli, 
behind these the tuberosity, in front of them the diastema; in the posterior 
border the maxillary hiatus leading to the superior dental, spheno-palatine and 
palato-maxillary foramina. 

3. The premaxilla; in the anterior border the incisor alveoli, in the inner 
border the incisive foramen, and projecting backward the palatine process. 

4. The malar; forms the antero-inferior part of the orbit, passing backward 
externally the zygomatic process and ridge. 

5. The lachrymal; in the supero-anterior part of the orbit, the upper border 
is the orbital ridge in the middle of which is the lachrymal tubercle; the pos- 



PHYSIOLOGY, COMPARATIVE ANATOMY 



terior surface has the lachrymal fossa which lodges the lachrymal gland anfl 
leads to the lachrymal canal. 

6. The palatine; placed beneath the posterior nares; in the middle is the 
spheno-palatine foramen; between the superior and nasal surfaces the crest; on 
the inferior surface which forms the arch, is the staphyline groove and a groove 
which helps to form the palatine foramen. 

7. The pterygoid; on the inferior surface of the sphenoid, terminates anteri- 
orly in a blunt process, the summit; the posterior extremity forming the Vidian 
canal. 

8. The vomer; forming the postero-inferior part of the nasal septum, has a 
gfoove in its upper border lodging the cartilaginous part. 

9. The turbinals; the upper attached to the nasal, the lower to the superior 
maxilla, divides the fossa into superior, middle and inferior meatuses. 

10. The inferior maxilla; has on the posterior the condyle, in front of this 
the coronoid process, and between these the sigmoid notch. In the upper border 
the molar alveoli, the interdental space, and anteriorly the incisor alveoli; in 
the outer surface the mental foramen, in the inner surface the inferior dental, 
leading to the dental canal. 

11. The hyoid series; the body has the spur process buried in the tongue; 
two heel processes articulating with the thyroid cartilages of the larynx; two 
cornicula rising from the body to the cornua; and the cornua which extend back- 
ward to articulate with the hyoid process of the petrosal bone. 

The Veitebral Column. 
<7^3. Ijumbar7^ijr segrherits, by long transverse processes ; the fifth by one"! 
A vertebra is one segment, described as true or false vertebra. 

1. A true vertebra has typical parts retained through life and does not unite 
with others by ossification in health. The typical parts of a true vertebra are: — 
Body, arch (pedicles and laminae) notches, and spinous, transverse and articular 
processes. 

2. A false vertebra lacks some of these parts or becomes united to others 
by ossification. 

Regions: — 1. Cervical, seven segments; known by greater size and length 
of body, and articular processes. Special segments: 

First. By glenoid cavities and rudimentary body. 

Second. By the odontoid process and prominent neural spine. 

Sixth. By short body and three tuberosities on transverse processes. 

Seventh. By absence of foramen in transverse process, and by facet for head 
of rib. 

2. Dorsal, eighteen segments; by long neural spines and facets for ribs, 
articular facet on each transverse process; sixth, by two facets on each transverse 
process. 

4. Sacral, five segments in the young, one in the adult; by union by ossifi- 
cation. 

5. Coccygeal, thirteen to twenty; by rudimentary form. 
Thorax: — Enclosed by the dorsal vertebra, ribs and sternum. 

1. The sternum; composed of six segments, united by cartilage in the young, 
by ossification in the adult; has on each side eight facets for articulation of the 
true ribs; prolonged anteriorly by the cariniform, posteriorly by the ensiform, 
cartilage. 

2. The ribs; eighteen on each side, eight of which are attached to the sternum 
by their cartilages, forming true joints, and known as true ribs; the ten posterior 
ribs are attached to the sternum by their cartilages overlapping each other, and 



VETERINARY ANATOMY, HISTOLOGY, 



known as false ribs. On the proximal extremity is the head having two facets 
separated by a groove; below this the neck; posterior to the neck the tubercle 
with a facet for articulation with the transverse process of the vertebra; below 
the neck the angle; a groove in the posterior border for the blood vessels and 
nerves and a facet in the distal extremity for the costal cartilage. 
Pectoral Llnib. 

1. Scapula; two surfaces, three borders, three angles; on the outer surface 
the spine, tubercle, antea and postea spinatus foss%; on the inner surface the 
subscapular fossa and nutrient foramen; on the anterior border the coracoid 
process, below it the neck and on the inferior angle the glenoid cavity; attached 
to the upper border the cartilage of prolongation. 

2. Humerus; on the proximal extremity the head, neck, internal trochanter 
with three prominences, the external with two, and between the trochanters the 
bicipital groove. The distal extremity is divided by a groove which terminates in 
the coronoid fossa in front and the olecranon fossa posteriorly; on the inner side 
a condyle, on the outer a trochlea; extending upward posteriorly the epicondyle 
and epitrochlea. The shaft has four surfaces; in the outer the musculo-spiral 
groove, between this and the anterior is the deltoid ridge and external tuberosity, 
on the inner surface the internal tuberosity and nutrient foramen. 

3. The radius; on the proximal extremity two glenoid cavities, bicipital 
tuberosity, external tuberosity and coronoid process; posteriorly two facets for 
the ulna. The distal extremity has three facets; on the anterior aspect two 
vertical and one oblique groove; laterally two prominences, the outer being 
marked by a vertical groove. The posterior surface has a rough triangular 
space for the ulna, above this a transverse groove assists in forming the radio- 
ulnar arch; and a ridge on the lower third of the internal border. 

4. The ulna; attached by ossification to the posterior surface of the radius; 
above the attachment a transverse groove, above this two facets. The part 
above the radius is the olecranon process, which has two surfaces, two borders 
and a summit; the inner surface is smooth and forms the external boundary of 
the carpal arch; the anterior border has a concave articular surface and a promi- 
nent process above, the beak. 

5. The carpus; eight bones arranged in two rows; the upper of which 
articulates with the radius, named from within outward, the scaphoid, lunar, 
cuneiform, and behind the last the trapezium; the lower row, articulating with 
the metacarpals, are the trapezoid, os magnum, unciform, and behind the first 
the pisiform. 

6. The metacarpi magnum; on the proximal extremity three facets, and 
anteriorly a tubercle, posteriorly a rough prominence, and on each border two 
facets for the splint bones; the distal extremity has two condyles separated by a 
ridge, laterally two depressions; the postero-lateral borders have two rough 
spaces for the splint bones. 

7. Splint bones (ossa metacarpi parva) : the outer has one facet superiorly, 
the inner, two; each having two facets on the inner surface of the head, and a 
rough space extending downward, terminating below in a small nodule. 

8. The OS suffraginis; on the proximal end two glenoid cavities separated 
by a groove; laterally two prominences. The distal end has two condyles sepa- 
rated by a groove, and on each side a depression; the posterior surface has a 
rough triangular space base upward. 

9. The OS coronae; on the upper surface two glenoid cavities separated by a 
••idge, at each end of which is a slight eminence; the lower surface has two 



PlfYSIOLOOY, COMPARATIVE ANATO»IY 



condyles separated by a groove; the posterior surface has a prominence cov- 
ered by fibro-cartilage. 

10. The OS pedis; the articular surface (upper) has two glenoid cavities 
separated by a ridge, and behind the cavities a narrow articular surface; the 
anterior surface (wall) is semi-circular, surmounting it the pyramidal process, 
on each side of which is a depression; the wall terminates posteriorly in the 
wings, which are divided by the pre-plantar fissure into a lower, retrossal, and 
an upper basilar process; the lower surface (sole) is semi-lunar, concave, and 
separated from the tendinous surface by the semilunar ridge; the tendinous sur- 
face is rough, triangular and has on each side the plantar groove which terminates 
in the plantar foramen. 

11. The OS naviculare; the upper and lower surfaces each have two facets 
separated by a ridge; the anterior surface a narrow facet. 

12. The sessamoid bones are two, of triangular shape, placed behind the 
fetlock joint, articulating with the metacarpi magnus, and forming a groove for 
the flexor tendons. 

The Pelvic Arch and IJmib. 

The arch formed by the os innominata; each of which is composed of three 
bones, the ilium, ischium and pubis. These with the sacrum enclose the pelvic 
cavity. 

1. The ilium; the upper anterior part of the arch, is broad; the external 
surface concave, the internal convex and rough for articulation with the sacrum; 
the anterior spine is a strong prominence which forms the point of the hip; the 
posterior spine meets its fellow over the sacral spines; the inner border extends 
from the posterior spine to the acetabulum where it forms the sciatic spine; the 
crest extends from the anterior to the posterior spine; the posterior angle forms 
two-fifths of the acetabulum, in front of which are two depressions in the narrow 
three-sided part (shaft) of the bone. 

2. The ischium; the posterior part of the arch, joins its fellow in the median 
line, the posterior borders forming the ischial arch, at the external angle of 
which is the tuberosity, and beneath it the inferior ischiatic spine; the ramus 
forms the inner, the body the posterior, and the shaft the outer boundary of the 
obturator foramen; the shaft at its anterior angle forms two-fifths of the 
acetabulum, and its upper border part of the sciatic (superior ischiatic) spine. 

3. The pubis; the antero-inferior part of the arch, lodges the urinary blad- 
der, extends to the cotyloid notch of the acetabulum, its lower surface grooved, 
its anterior border (crest) joining a ridge on the lower surface of the ilium, 
forming the ilio-pectineal line; the posterior border forms the anterior border 
of the obturator foramen. 

The acetabulum (cotyloid cavity) receives the head of the femur, has a 
depression in the floor and a notch in its inner border. 
Pelvic Liimb. 

1. The femur; on the proximal extremity is the head, neck, trochanter major 
with a summit and convexity; trochanteric fossa and ridge; on the distal extrem- 
ity two condyles separated by the inter-condyloid groove, on the outer two 
depressions, on the inner a rough prominence; anterior to the groove a trochlea 
and between it and the external condyle a deep fossa. The posterior surface is 
marked by two rough spaces and a ridge superiorly, and the supracondyloid 
fossa and crest inferiorly; the external border a prominent ridge and on it the 
trochanter minor; the inner border the trochanter internus and a ridge from it 
to the head, another ridge extending downward. 

2. The tibia; on the upper extremity two broad articular surfaces, a spine 



8 VETERINARY ANATOMY, HlSTOIX)GY, 

and a depression; anteriorly a tuberosity, externally a facet and between this and 
the tuberosity a deep groove; internally a tubercle. On the distal extremity two 
deep grooves separated by a ridge, bounded laterally by the prominent malleoli, 
the outer being grooved; the tibial ridge on the upper third of the anterior border 
joins the tuberosity above. 

3. The fibula; rudimentary, has on the inner side of the head a facet; the 
space between this bone and the tibia is the tibio-fibular arch. 

4. The tarsus; composed of six bones; the os calcis forming the point of the 
hock; the astragalus, with the tibia forming the true joint, rests on the cuneiform 
magnum, it on the medium, with the parvum internally and the cuboid extern- 
ally, the last three articulating with the metatarsal bones. 

5. The metatarsi magnum; on the upper extremity three facets and a fossa; 
the bone resembles the metacarpal, as do also the splint bones, and the digit. 

6. The patella; a large sessamoid bone developed in the tendon of the 
extensor muscles articulates with the trochlea of the femur. 

II. HISTOLOGY OF THE BONE. 

Structure: — Bone is composed of earthy matter (principally lime salts) 67 
per cent., and animal matter (collagen) 33 per cent., so intimately blended that 
either may be removed by heat or chemicals without changing the shape. To 
the eye bone appears in two forms; compact, a hard ivory-like substance form- 
ing the shaft of long bones and the external shell of all others; and cancellous, 
a spongy substance forming the inner mass of all except the shaft of long bones. 

1. By the microscope compact bone is seen to contain channels, (Haversion 
canals) which anastomose, and are surrounded by concentric lamellae, the whole 
called a Haversion system. The spaces between these systems are filled bv 
interstlcial lamellae; a set of lamellae covers the bone externally, another lining 
the marrow cavity, called the outer and inner circumferential lamellae. Scat- 
tered between the lamellae are spaces (lacunae) communicating with each 
other, the Haversion canals, marrow cavities and subperiosteal tissue, by minute 
channels (canaliculi). Openings in the circumferential lamellae (Volkmann's 
canals) convey blood vessels to the Haversion canals, each of which contains 
an artery or vein or botli; the vessels are surrounded by perivascular spaces 
lined by endothelial cells resting on the outer coats of the vessels ana wans of 
the canals. These spaces communicate by means of the canaliculi, with the 
lacunae, and lymph spaces of the periosteum and marrow cavities; by this means 
a constant flow of lymph plasma passes through the lacunae, in each of which 
is lodged a bone cell, its processes extending into the canaliculi. 

2. Cancellovis bone; forming the inner mass of all except the shaft of long 
bones, is a frame work of bone fibers in which is lodged red bone marrow, blood- 
vessels, nerves and lymphatics. 

3. Covering of bone is a tough canvass-like membrane, having an external 
fibrous, and an inner vascular bone forming layer, the osteogenetic membrane. 

4. Development. Bone is developed in two ways; in cartilage and in mem- 
brane. 

a. Endochondral bone. 

All the bones of the adult body, excepting those of the vault of the skull 
and the face, are in foetal life pre-formed in embryonic cartilage. This changes 
to hyaline, then the cells enlarge at the expense of the matrix and become ar- 
ranged in rows; calcareous granules are deposited in the thinned walls of the 
matrix; the cells are thus cut off from nutrition and disappear, leaving spaces 



PHYSIOLOGY, OOaiTAKATIVE ANATOMY 9 

(primary narrow spaces) surrounded by walls of calcified cartilage matrix. 
While this change is taking place in the cartilage a thin layer of bone is de- 
posited on its surface by the osteogenetic layer of the perichondrium (which now 
becomes .the periosteum) and through this bony shell the osteogenetic layer 
sends bud-like process into the cartilage; these buds consist of bone-destroying 
cells (osteoclasts) and bone-forming cells (osteoblasts). The osteoclasts absorb 
the calcareous partitions between the primary marrow spaces, forming secondary 
marrow spaces (Haversion spaces); into these spaces blood-vessels are pushed; 
osteoblasts now deposit layer after layer of bone (lamellae) on the inner wall 
of the spaces until a small channel (the Haversion canal) remains, the blood- 
vessels of the marrow spaces becoming the vessels of the Haversion systems. 
The large marrow cavity in the shaft of adult long bones is formed during de- 
velopment by the absorption of the embryonic bone (by osteoclasts), many of 
the lamellae first laid down by the periosteum are thus absorbed; as new layers 
from the outer surface increase the thickness of the wall the osteoclasts remove 
those first formed from the inner, until the permanent marrow cavity is formed. 
By this process the entire shaft of adult bone, which began as endochondral bone, 
is changed to bone formed in membrane (intramembranous). Ossification of 
cartilage and membrane begins at points called centers of ossification. The 
shaft of long bones (diaphysis) begins in the center, ossification extending to- 
ward the extremities, the ends of long bones begin at one or more centers, ossi- 
fication extending in all directions. As the osseous tissue developed in the ends 
(epiphyses) approaches that in the diaphysis, there remains a zone of hyaline 
cartilage in which ossification is long delayed; at this point the perichondrium 
is thickened, projecting into the cartilage forming a depression (the ossification 
groove) the ridge filling it, the ossification ridge. This delay admits of the 
growth of bones in length, as bone tissue takes the place of cartilage at the ends 
of the zone new cartilage is formed by the perichondrium, the process continu- 
ing until the bone has reached full development. 

b. Intramembranous bone. 

As in the endochondral, this begins at a center of ossification, from which 
spicules of soft transparent substance (osteogen) shoot out in all directions, 
and are called osteogenetic fibers. On and around these calcareous granules 
are deposited until they become spicules of bone; this process extends until a 
thin lamella of bone is formed, the fibers interweaving (the intercrossing fibers 
of Sharpey). As new lamellae are added other fibers pierce the layers, binding 
them together (perforating fibers of Sharpey). The reticulated tissue of spongy 
bone is developed by osteoblasts becoming arranged about fibrous tissue bundles, 
forming large meshes of irregular osseous trabeculae enclosing marrow spaces 
in which the red bone marrow is lodged. 

5. Bone marrow, red and yellow. 

The buds which carry bone forming elements into the cartilage also carry 
marrow forming elements. The red marrow is first formed, consisting of cellu- 
lar elements in a matrix of recticular tissue, surrounded by a fibrous mem- 
brane, the endosteum, and containing numerous vessels. The cells are: 

1. Myelocytes (marrow cells). 

2. Nucleated red blood cells, called erythroblasts, from which are developed 
normoblasts, also nucleated. While yet in the marrow or in its venous spaces 
the nuclei are extruded, the non-nucleated red blood cells resulting. 

3. Cells with eosinophlle granules. 

4. Cells with basophilic granules. 



10 V^ETERINARY ANATOMY, HISTOLOGY, 

5. The various forms of leucocytes and lymphocytes found in blood and 
lymph. 

6. Giant cells, or myeloplaxes. 

Yellow marrow is derived from red marrow by a change of its cells to fat 
cells, is found principally in the shaft of long bones, and is not a blood forming 
organ. 

III. PHYSIOLOGY OF BONE. 

The bones of the extremities form pillars of support, and levers by which 
the body clianges position and moves from, place to place. Plat bones enclose 
and protect vital organs; while the bony skeleton forms the foundation on which 
the entire body is built. By the marrow it is also an important organ in the 
development and elaboration of the blood. 

CHAPTER II. 

ARTICULATIONS. 

Joints: — Two or more bones united to each other by fibrous or cartilaginous 
structures form a joint. 

There are three classes of joints: 

1. Immovable or synarthrodial. 

a. Sutura I. S. Vera, the margins unite by interlocking processes. 
S. Vera, Dentata with tooth like processes. 

S. Vera, Serrata with fine saw like processes. 

S. Vera, Limbosa, the margins are dentated and bevelled. 

2. S. Notha, the margins unite by plain rough surfaces. 
S. Notha Squamosa, the margins are bevelled and overlap. 

S. Notha Harmonia, the margins unite with no irregularities. 

b. Synchondrosis. Sutura united by cartilage instead of fibrous tissue. 

c. Schindylesis. A plate of one bone is received in a slit of another. 

d. Gomphosis. A process of one bone is set in a socket of another. 

2. Movable or diarthrosis. True joints. 

a. Arthrodia. Motion is slight and gliding. 

b. Enarthrosis. Motion in all directions; ball and socket joint. 

c. Ginglymus. Motion in one plane only; hinge joint. 

d. Rotatory. Motion limited to rotation; pivot joint. 

3. Amphiarthrosis. Mixed joint; this term refers to the structure, the bones 
being united by a pad of fibro-cartilage. 

Motion:—!. Extension. The bones approach more nearly a straight line. 

2. Flexion. The bones form a more acute ansle. 

3. Abduction. The limb is moved from the central plane. 

4. Adduction. The limb is moved toward the central plane. 

5. Rotation. The limb or bone rotates on its own axis. 

6. Gliding. One bone glides over another, always very limited. 

7. Circumduction. The distal extremity of the limb describes a circle. 
LiS^aments:^ — Are binding structures of white fibrous tissue, in a few cases 

of vellow elastic tissue. 

1. Capsular ligaments surround and enclose joints, are lined by a serous 
membrane, and synovial glands. 

2. Lateral ligaments are thickened portions of capsular, binding the bones 
of an articulation together. 

3. Annular are thickened portions of capsular ligaments or fascia binding 
down tendons where they cross over joints. 



PHYSIOLiOGY, COIVIPAIIATIVE ANATOMY 11 

4. Check ligaments originate on bones and are attached to tendons of mus- 
cles, limiting their motion. 

SjTiovial membranes (glands): — Are placed wherever lubrication of joints 
and tendons is necessary. 

1. Capsular, within capsular ligaments. 

2. Bursal, around points over which tendons move. 

3. Vaginal, in sheaths through which tendons pass back and forth. 
Synovia: — Is a viscid lubricating fluid secreted by these glands. 
Cartilage: — Is a form of connective tissue, of various kinds. 

1. Hyaline: 

a. Articular, covering the articular surfaces of bones. 

b. Costal, prolongations on distal extremities of ribs. 

c. Membraniform, in plates or sheets as in the trachea. 

2. Fibro-cartilage: 

a. Interarticular (meniscus), a pad between bones of a true joint. 

b. Connecting, the bond of union in mixed joints. 

c. Stratiform (investing), covering points of bone over which tendons glide. 

d. Curcumferential, deepens articular cavities. 

Articulations of tlie skeleton: — The bones of the skull and face are united 
by immovable joints, the temporo-maxillary only being a true joint, with a men- 
iscus, capsular, posterior and external lateral ligaments. ^ 

Hyoitl series: — The temporo-hyoid and proximal inter-hyoid and thyro-hyoid 
are mixed joints. The distal inter-hyoids are true joints. 

Vertebral: — The occipito-atloid is a true joint with capsular," 2 lateral, (sty- 
loid) and superior and inferior suspensory ligaments. The atlo-axoid a true 
joint with capsular, superior and inferior odontoid. The 5th and 6th lumbar 
and last lumbar and sacrum form true joints by facets on their transverse pro- 
cesses, with capsular ligaments. The centra of the remaining vertebrae unite 
by mixed joints, the oblique processes by true joints with capsular ligaments. 
Ligaments of the vertebral column are superior and inferior common, supra- 
spinous, inter-spinous, inter-transverse, ligaments of the arches, and ligamentum 
nuchae. The last two are yellow elastic tissue. 

Thoracic: — Costo-vertebral; two true joints between head of rib and body of 
vertebra, one between tubercle of rib and transverse process, with three capsular, 
stellate, round, anterior and posterior transverse. The chondro-costal is a gom- 
phosis. The costo-sternal a true joint with capsular, superior and inferior costo- 
sternal. The sternal segments unite by fibro-cartilage which ossifies in old age. 

Pectoral Unib: — 1. Scapulo-humeral; capsular only; tendons passing over it 
acting as ligaments. 

2. Humero-radio-ulnar; capsular, internal and external lateral. 

3. Radia-ulnar; superior and inferior radiating and interosseous. 

4. The carpus; special ligaments are: 

a. Superior carpal (between bones of upper row) 3 anterior and 3 inter- 
osseous. 

b. Inferior carpal (between bones of lower row) 2 anterior and 2 inter- 
osseous. 

c. Radio-carpal (between radius and bones of upper row) oblique, superior 
trapezial, and a small one beneath it. 

d. Inter-carpal (between the upper and lower rows) the inferior trapezial 
and two short ones under the posterior common ligament. 

e. Carpo-metacarpal (between the lower row and the meta-carpal bones) 2 
anterior, 2 posterior, and 2 interosseous. 



12 VETEKUVARY ANATOaiY, HISTOIiOGY, 

The common ligaments are: External and internal lateral, anterior and pos- 
terior common, or capsular. 

5. Metacarpo-phalangeal; capsular, 2 lateral, superior sessamoidean (sus- 
pensory), inferior sessamoidean (X. T. V.), lateral sessamoidean, inter-sessa- 
moidean, and annular. 

6. Proximal inter-phalangeal: 2 lateral, 2 posterior and capsular. 

7. Distal inter-phalangeal; capsular, antero- and postero-lateral; and broad, 
lateral and inferior navicular ligaments. 

Pelvic Arch: — Sacro-iliac; superior, inferior and lateral sacro-iliac, sacral, 
and sacro-sciatic ligaments. 

Pelvic liimb: — 1. Femoro-pelvic: capsular, round, transverse, pubio-femoral 
and cotyloid. 

2. Femoro-tibial: two menisci, 5 coronary, 2 crucial, 2 lateral and capsular. 
Patellar group, capsular, 2 lateral, 3 straight. 

3. Tibio-fibular: capsular and 2 interosseous. 

4. The tarsus: common are capsular and 2 lateral. Special are: superior 
(between astragalus andos calcis) ; 1 superior, 2 lateral and 2 interosseous. In 
ferior tarsal; 2 anterior, 3 interosseous. Inter-tarsal; calcaneo-cuboid, oblique, 
tarso-metatarsal, great interosseous. Posterior and anterior annular. The ar- 
ticulations and ligaments below the tarsus are the same as in the pectoral limb. 

Tendons and ligaments are the densest variety of fibrous connective tis- 
sue. Formed of bundles of white fibrils in parallel courses, called tendon fasci- 
culi, the fibers cemented by an inter-fibrillar cement substance. The fasciculi 
branch at acute angles and anastomose with other fasciculi. These fasciculi are 
grouped to form secondary tendon bundles, united by the inter-fascicular ground 
substance, in which there are cell spaces occupied by the tendon cells arranged 
in rows between the fasciculi, and having wing-like processes passing between 
the fasciculi. The secondary bundles are grouped to form the tendon, the whole 
held together and surrounded by areolar tissue, the peritendineum. From this 
septa pass in between the secondary bundles, and are called the internal periten- 
dineum, along which the nerves and bloodvessels reach the interior of the tendon. 

Elastic fibrous tissue (found in the ligamentum nuchae and subflava) is a 
tissue in which the elastic fibers predominate over the white fibers. 

CHAPTER III. 

ANATOMY OF MUSCLES. 

The voluntary movements of the body are accomplished by the action of 
contractile tissue, called striated muscle. The movements of the vital organs are 
controlled by a contractile tissue called plain or non-striated muscle. The first 
receives its nerves from the cerebro-spinal system and is under control of the 
will. The latter receives nerves from the sympathetic system, its movements be- 
ing involuntary. 

1. Voluntary Muscles: 

Muscles are named and described according to shape, position or action, and 
as having a point of origin (usually the least movable attachment) and a point 
of insertion, either of which may be a bone, tendon, skin, or fibrous structure. 
Tendons are fibrous prolongations by which muscles are attached, and their 
action transmitted, to parts more or less distant from the contractile tissue. 
Aponeuroses are weblike expansions of fibrous material acting as tendons to 
muscles of broad outline, as the abdominals. Fascia is fibrous membrane vary- 
ing in thickness, covering the body under the skin, enveloping each muscle, ten- 



PHYSIOLOGY, COMPARATIVE ANATOMY 13 



don, nerve, etc. The voluntary muscles are arranged in regions. 1. The sub- 
cutaneous, one muscle, the paniculus carnosis, covering the neck, sides of face, 
shoulders and thorax. 2. Head. 3. Trunk. 4. Pectoral limb. 5. The pelvic 
limb. Each region is subdivided into groups. 

Head. 

1. Anterior maxillary. 

Zygomaticus. 

0. Fascia of masseter. 

1. Angle of mouth. 

■ A. Retracts angle of mouth. 
Orbiculaiis oris. 

0. Skin around mouth. 

1. Same. 

A. Controls action of mouth, and gives attachment to other muscles. 
Buccinator. 

0. Alveolar tuberosity, alveoli and interdental spaces. 

1. Same as origen. 

A. Control of food in mastication. 
Levator L. S. A. N. 

0. Junction of frontal and nasal bones. 

1. Nostril, upper lip and angle of mouth. 

A. Dilates nostril, raises upper lip and angle of mouth. 
Nasalis longus. 

0. Junction of maxilla, malar and lychrymal bones. 

1. With its fellow in upper lip. 

A. Together raise upper lip, alone draw it to one side. 
Dilator naris later's. 

0. Anterior extremity of maxillary spine. 

1. Side of nostril and upper lip. 
A. Dilates the nostril. 
Dilator N. Infre's. 

0. Upper free niargin of superior and pre-maxillae. 

1. Skin of false nostril. 
A. Dilates the nostril. 
Dilator N. Ti'ansv's. 

O. Nasal peak. 

T. Upper border of alae of nostril. 

A. Dilates nostril. 

Dilator N. Super's. 

0. Free margin of nasal bone. 

1. Skin of false nostril. 
A. Dilates nostril. 
Depressor. Labii Sup'. 

0. Alveoli of pre-maxillae. 

1. Upper lip and nasal cartilages. 
A. Compresses the upper lip. 
Depressor Labii luf' . 

0. Alveolar tuberosityand border of inferior maxilla. 

1. To lower lip. 

A. Depresses lower lip. 

Levator Labii Inf'. 

O. Alveoli of inferior maxilla, near incisors. 



14 VETERINARY ANATOIMY, HISTOLOGY, 

1. To lower lip. 

A. Elevates lower lip and chin. 

2. Posterior maxillary group. 
Masseter. 

0. Zygoma and spine and external surface of superior maxilla. 

1. Outer surface, posterior border and angle of inferior maxilla. 
A. Closing lower jaw on upper, powerful muscle of mastication. 
TeniiK>ralls : 

0. Parietal bone and ridge, zygoma, and occipital crest. 

1. Coronoid process of inferior maxilla. 

A. Together closes lower jaw, alone gives it lateral motion. 
Stylo-MaxlUaris : 

0. Styloid process of occiput. 

1. Posterior angle and margin of inferior maxilla. 
A. Depresses and retracts lower jaw. 
Pterygoid inleinus: 

0. Pterygoid process and palatine ridge. 

1. Inner posterior border and angle of inferior maxilla. 

A. Together rai.scs and closes lower jaw, alone gives it lateral motion. 
Plcrygoid exlernus ; 

0. Ala and pterygoid process of sphenoid. 

1. Inner side of inferior maxilla, below condyle. 
A. Assists internus and draws jaw forward. 
Digastricus : 

0. Styloid process of occiput. 

1. Inner siwface of inferior maxilla near symphisis. 

A. Retracts and depresses lower jaw, elevates hyoid bone. 

3. Hyoidean. 
Mylo - hyoideiis : 

0. A line below alveoli of inferior maxilla, 'hyoid bone. 

1. Meets its fellow in median line under the tongue. 
A. Supports, elevates and draws the tongue forward. 
Genlo-hyoideniis : 

0. Inner surface inferior maxilla near symphistis. 

1. Spur process of hyoid. 

A. Draws hyoid bone downward and forward. 
Hyoideus magnus: 

0. Postero-inferior angle of hyoid cornu. 

1. Tubercle on heel process of hyoid bone. 
A. Draws hyoid upward and backward. 
Hyoideus i)ar\iis: 

0. In angle of cornu and corniculum. 

1. Body and heel process of hyoid. 
A. Approximates hyoid series. 
Hyoideus transversus: 

0. Corniculum of hyoid. 

1. To corniculum of opposite side. 
A. Approximates cornicula. 

Stylo - hyoideus : 

O. Styloid process of occiput. 

I Posterior part hyoid cornu. 

A. Draw hyoides downward and backward. 



PHYSIOLOGY, COlVIPiVRATIVE ANATOMY J5 



4. Palpebral. 
Orbicularis palpebrarum: 

0. Circular muscle surrounding orbit. 

1. To lachrymal tubercle and skin. 

A. Assists in closing the eye. Very small, unimportant. 
L*achrynialis : / 

0. Frontal bone near supra-orbital foramen. 

1. Blends with orbicularis palpebrarum. 
A. Corrugates upper eye lid. 

Levator palpebrae sup' ext' Jj. P. sup' internus: 

0. Superior border optic foramen. 

1. Inner surface upper lid and tarsal cartilage. 
A. Raises upper lid. 

5. Auricular. 
Attolens Maxlnius: 

0. Parietal crest. 

1. Scutiform cartilage. 

A. Adducts and elevates the ear and turns the opening forward. 
Attolens Antieus: 

0. Zygomatic process of temporal. 

1. Anterior part of scutiform and base of conchal cartilage. 
A. Draws ear forward. 

Attolens posticus: 

0. Parietal crest and temporal muscle. 

1. Posterior surface of concha near base. 
A. Elevates and adducts the ear. 
Ketrahens externus: 

0. Cord of ligamentum nuchae. 

1. Posterior surface of concha. 

A. Draws ear backward and downward. 
Ketrahens niedius: 

0. Same as externus. 

1. Base of concTia externally. 

A. Turning opening of ear backward. 
Ketrashens Intemus : 

0. Same as medius. 

1. To dilated part of concha. 
A. Same as medius. . 
Mastoido-Aui'icularis : 

0. External auditory meatus. 

1. Base of concha. 

A. Draws concha downward. 
Abtlucens : 

0. External surface of parotid gland. 

1. Base of concha externally. 

A. Draws ear downward and outward. 

Scuto-auiicularis, externus and internus are unimportant. 
Region of Tnink: 
I. Inferior cervical. 

Stemo Maxillaris : 

0. Anterior part of cariniform cartilage. 

1. Angle of lower jaw. 



16 VETERINARY ANATOMY, HISTOLOGY, 

A. Together draw the head downward, singlj' draws it to one side. 
Sterno-thyro hyoitleiis : 

0. Superior part cariniform cartilage. 

1. By one tendon to hyoid cartilage, another to hyoid, spur process. 
A. To depress hyoid, larynx and base of tongue. 

Siibscajmlo hyoitleiis: 

0. Subscapularis fascia. 

1. Spur orocess of hyoid. 

A. To depress the hyoid apparatus. 
Rectus cap' ant' major: 

0. Transverse processes 3rd. 4th, and 5th cervical vertebrae. 

1. Basilar process of occiput and body of sphenoid. 

A. Together draw the head downward, singly draws it to one side. • 
Rectus cap' ant' minor: 

0. Body of the atlas. 

1. Same as major. 
A. Flexes the head. 
Rectus cap' lateralis: 

0. From the wing of the atlas. 

1. To styloid process of the occiput. 
A. Same as the preceding. 
Scalenus : 

0. Transverse processes last four cervical vertebrae (anter'rpart). 

1. Anterior and outer border of first rib. 

0. Transverse processes last 3 or 4 cervical (posterior part). 

1. Upper part of first rib. 

A. Draws first rib forward, when rib is fixed extends the neck. 

liongus colli: 

O. Lower surface of bodies of first six dorsal, and inferior spines and trans- 
verse processes of last six cervical. 

I. Inferior spine of atlas and axis. 
A. Draws neck downward. 

2. Lateral cervical. 
Levator humei-i: 

0. Crest of occiput, mastoid process, wing of atlas, transverse processes of 
2nd, 3rd and 4th cervical and fascia of neck. 

1. To fascia of arm and a line on humerus below the deltoid ridge. 

A. Together depress the head, singly turns it to one side; when the neck 
is fixed advances the limb. 
Trapezius : 

0. Cord of the ligamentum nuchae. 

1. Spine, tubercle and fascia of scapula. 

A. Elevates and draws the shoulder forward. 
Rhomboideus L(On2:us : 

0. Cord of ligamentum nuchae up to second cervical. 

1. Inner surface of anterior angle of scapula, and cartilage above. 
A. Elevates and draws the scapula forward. 

Splenius: 

0. Cord of ligamentum nuchae, transverse process of third, fourth and 
fifth cervical, and spines of first five dorsal. ^ 

1. To wing of the atlas and mastoid ridge and crest. 
A. Together elevates the head, singly draws it to' one side. 



PHYSIOLOGY, COMPARATIVE ANATOMY 17 

Ti'achelo Mastoideus : 

0. Transverse processes of first two dorsal, and oblique processes of the last 
five cervical. 

1. By two tendons, to wing of atlas and mastoid ridge. 
A. Together raise the head, singly draws it to one side. 
Coniplexus Major: 

0. Traverse and spinous processes of first five dorsal, oblique processes of 
all the cervical. 

1. To the side of the occipital tuberosity. 
A. Extends the head. 

Oomplexus Minor: 

0. The neural spine of the dentata. 

1. With the tendon of the major. 
A. Assitst the complexus major. 
Rectus Capitis Posticus Major: 

0. Neural spine of dentata. 

1. Occiput, in depression below the tuberosity. 
A. Extends the head. 

Rectus Capitis Posticus Minor: 

0. Supero-anterior part of the atlas. 

1. Below the major. 
A. Extends the head. 
Obliquus Capitis Anticns: 

0. Anterior edge of wing of atlas. 

1. Mastoid crest and styloid process of occiput. 

A. Together extend the head, singly, flex it laterally on the atlas. 
Obliqvius Capitis Posticus: 

0. Superior spine and side of dentata and capsular ligament. 

1. Upper surface of body and wing of atlas. 

A. Rotates the head, turning atlas on the dentata. 
Spinalis Colli: 

0. Oblique processes of first dorsal and last five cervical. 

1. Neural spines of all the cervical but the first. 
A. Extends and curves the neck. 
Intertransversalis Colli : 

0. Oblique process of one cervical vertebra. 

1. To transverse process of next anterior cervical vertebra. 
A. To flex the neck laterally. 

3. Costal Group. 
Trapezius Dorsalis: 

0. Supra-spinous ligament and dorsal spines from third to tenth. 

1. Tubercle on spine of scapula. 

A. Draws the scapula upward and backward. 
RJiomboldeus Brevls: 

0. Pleural spines of first five dorsal and supraspinous ligament above, 

1. Inner surface, upper border of scapula and cartilage above it. 
A. Draws scapula upward. 

Latissinius Dorsi. 

0. Neural spines and supra-spinous ligament, fifth dorsal to last lumbar. 

1. Internal tuberosity of humerus. 

A. Elevates the humerus, flexes shoulder, assists expiration. 
Serratus Magnus: 



18 VETERINARY ANATOMY, HLSTOIiOGY, 

0. Transverse processes of last five cervical, external surface of eight 
true ribs from the middle to their cartilage. 

1. Inner surface of scapula below the cartilage. 

A. Together suspend the body between pectoral limbs, depress the scapula, 
elevate the neck, assist inspiration. 
Superficialis Costariun: 

0. Dorsal spines second to thirteenth and supraspinous ligament. 

1. Fifth to thirteenth ribs below the angles, (anterior portion.) 

0. Spines of last eight dorsal and first lumbar. 

1. Posterior border last nine ribs, (posterior portion.) 

A. Anterior part inspiratory; posterior part expiratory, muscle. 
Transvei'salis Ctostarum: 

0. Transverse process of first lumbar and the ribs near their tubercles. 

1. External surface of all the ribs and the last cervical vertebra. 
A. Assists in expiration. 

Lievatores Costaruin: 

0. Transverse processes of dorsal vertebrae. 

1. External surface of ribs above the angle. 
A. Draws ribs forward in inspiration. 
External Iiitercostals : 

0. Posterior border of each rib above the cartilage. 

1. Anterior border of next posterior rib. 
A. Inspiratory muscle. 

Internal Intercostals: 

0. Anterior border of each rib below the angle. 

1. To posterior border of next anterior rib. 
A. Inspiratory muscle. 

4.. Pectoral Group. 
Pectoralis Traiisversiis: 

0. First four bones of the sternum. 

1. Olecranon process, anterior part of humerus, and fascia of inner arm. 
A. Adduct the arm and tense the brachial fascia. 

Pectoralis Magnus: 

0. Last four bones of sternum, ensiform cartilage, cartilages of false ribs, 
abdominal fascia and tunic. 

1. Inner trochanter of humerus, outer trochanter by fascia, and fascia of 
inner side of arm. 

A. Adducts the arm, draws shoulder back, assists inspiration. 
Pectoralis Anticiis: 

0. Cariniform cartilage and first bone of sternum. 

1. Anterior surface of humerus. 
A. Adducts the arm. 
Pectoralis Parvvis: 

O. First :^our bones of sternum, Cariniform cartilage, first four ribs and their 
cartilages. 

I. Fascia of shoulder and anterior border of scapula. 

A. Draws shoulder backward and downward. 

The pectoral group assists to support the body as in a sling. 

5. Dorso-Liumbar Group: 

LiOnglsstmus Dorsi: 

O. Crest, inner surface and supero-anterlor spine of ilium, spinous and trans- 
verse processes of first two bones of scrum; spinous, transverse and oblique pro- 



PHYSIOLOGY, C03IPAKATIVE ANATOMY 19 

cesses of all the lumbar; spinous and transverse processes of all the dorsal. 

I. External surface of last sixteen ribs, spinous and transverse processes of 
last four vervical vertebrae. 

A. Together used in rearing and kicking, singly, flex back and loins laterally. 
Spinalis Dorsl. 

0. First six dorsal spines, supraspinous ligament back to twelfth. 

1. Superior spines of last four cervical. 
A. Elevates the neck. 

Several small unimportant muscles are here omitted. 

6. Abtlominal Group: 

The linea alba is a strong fibrous cord attached to the ensiform cartilage 
anteriorly and to the pubic symphisis posteriorly; the aponeurosis of all the 
abdominal muscles meet in it. 

The abdominal tunic is a strong web of elastic tissue covering the abdominal 
muscles infero-laterally. 

External Oblique: 

0. Outer surface last fourteen ribs below the middle; anterior iliac spine and 
crest and lumbar fascia. 

1. To pubis, prepubian tendon and linea alba, 

A. To support and compress abdomen in defecation, urination and parturi- 
tion; flex vertebral column, and assist expiration. 
Internal Oblique: 

0. Anterior iliac spine, transverse processes of three first lumbar, fascia 
of latissimus dorsi and cartilages of false ribs. 

1. Symphisis pubis, prepubian tendon and linea alba. 

A. Assists the external oblique and draws last rib backward. 
TransA'crsalis Abdominis. 

0. Transverse processes of lumbar, cartilage of false ribs, inner side. 

1. To zyphoid cartilage and linea alba. 
A. Assists the oblique muscles. 
Rectus Abtlo minis: 

0. Inferior surface xyphoid cartilage and sternum, cartilages of last four 
true, and first two false ribs. 

1. By prebubian tendon to crest of pubis, and to linea alba. 

A. Support and compress abdomen, flex vertebral column, assist respiration. 

7. Siiblumbar Group: 
Psoas Magnus: 

0. Inner surface of last two ribs, bodies of last two dorsal, bodies and 
transverse processes of first five lumbar. 

1. Internal trochanter of femur. 

A. Flex and rotate the thigh, when thigh is fixed to flex the loins. 
Psoas Pai'vus: 

0. Bodies of last four dorsal and all the lumbar. 

1. Ileo-pectineal eminence. 

A. To arch the back and flex the pelvis on the vertebral column. 
Iliacus : 

0. Lower surface of ilium, ilio-pectineal ridge, inferior sacro-iliac ligament, 

1. Internal trochanter of femur. 

A. Flex and rotate the femur outward. 

Quadratus Lumborum: 

O. Inferior sacro-iliac ligament. 



20 VETERINARY ANATOMY, HISTOLOGY, 

I. Transverse processes of lumbar, posterior border and lower surface of last 
three ribs. 

A. Flex loins laterally, draw last rib back. 

8. Diaplii'agni: 

O. Right pillar, from bodies of first five lumbar. Left pillar from bodies 
of first two lumbar. Fleshy expansion from distal extremities of last twelve 
ribs and their cartilages, all converging to a tendinous center. 

A. Increases the antero-posterior diameter of tnorax in inspiration. 

9. Coccygeal Group: 
Erector Coccygis: 

0. Summit and sides of sacral spines and upper surface of coccyx. 

1. To bones of coccyx. 

A. Together elevate the tail, singly draws it to one side. 
Depressor Coccygis: 

0. Inferior surface of sacrum, sacro-siatic ligament and bones of coccyx. 

1. By tendons to lower surface of all the bones of the coccyx. 

A. Together depress the tail, singly draw it to one side and downward. 
Curvator Coccyx. 

0. Spines of last lumbar, sides of sacral and coccygeal segments. 

1. Side of coccygeal segments. 
A. Draws tail to one side. 
Compressor Coccygis: 

0. Superior ischiatic spine and sarco-sciatic ligament. 

1. Last sacral and first two coccygeal segments. 
A. Depress the entire tail. 

Region, Pectoral Limb. 

1. ExteiTial Scapular Group: 

Teres Externus: 

0. Two heads; 1. Posterior border and angle; 2. Tubercle on spine of 
scapula. 

1. Deltoid ridge of humerus. 

A. Abduct and rotate the humerus outward; with internus to flex the 
shoulder. 

Antea- Spina tus : 

0. Anterior angle, border and fossa of scasula. 

1. To summit of internal and external trochanters of humerus. 
A. Extend the humerus on the scapula. 

Postea - Spinatus : 

0. Posterior fossa, border and cartilage of prolongation of scapula. 

1. One tendon to the convexity, one below the summit of the external 
trochanter of the humerus. 

A. Abduct and rotate the humerus outward. 
Postea- Spinatus Minor: 

0. Posterior border, fossa, and tubercle near glenoid cavity. 

1. Deltoid ridge of humerus. 
A. Same as postea spinatus. 

2. Internal Scapular Group: 
Teres Internus: 

O. Posterior border and angle of scapula. 
I. Internal tuberosity of humerus. 
A. Adduct and rotate the humerus inward, with the externus to flex it. 



PHYSIOLOGY, OOatPARATIVE ANATOMY 21 

Subscapularis: 

0. Subscapular fossa. 

1. Posterior prominence on internal trochanter of humerus. 
A. Adduct the arm'. 

Scapulo-Huineralis Posticus: 

0. Capsular ligament of shoulder, and posterior border of scapula. 

1. Posterior surface of humerus below the head. 
A. Tense the capsular ligament. 

3. Anterior Brachial Group: 
Coraco-Raclialis : 

0. Coracoid process of scapula. 

1. Bicipital tuberosity; by fascia to extensor metacarpi magnus. 

A. liibctend the shoulder, flex the eldow, and tense the brachial fascia. 
Coraco-Hunieralis : 

0. Beak of coracoid process of scapula. 

1. By two tendons to the shaft of the humerus, one above and one below 
the internal tuberosity. 

A. Extend, adduct and rotate the arm inward. 
Humeralis Obliquiis: 

0. Posterior surface of humerus below the head, musculo-spiral groove. 

1. Inner side of radius, and arciform ligament of ulna. 
A. Flex the elbow. 

4. Posterior Brachial Group: 
Scapulo - Ulnaris : 

0. Posterior border and angle of scapula. 

1. Apex of olecranon, and anti-brachial fascia. 

A. Flex the shoulder, extend the elbow and tense the fascia. 
Caput Magnum: 

0. Posterior border and angle of scapula. 

1. Inner, upper part of olecranon. 

A. Flex shoulder and extend forearm. 
Caput Mediiun: 

0. Shaft of humerus from deltoid ridge to the neck. 

1. Supero-posterior part of olecranon. 
A. Extend the forearm. 

Caput Painuni: 

0. Postero-internal surface of humerus, middle third. 

1. To apex of olecranon. 
A. Extend the forearm. 

Anconeus: 

0. Borders of olecranon fossa and capsular ligament. 

1. Antero-external part of olecranon. 
A. Tense capsular ligament. 

5. Anterior Anti-Brachial Group: i 
Extensor MetacaiTJi Magnus: 

0. Epitrochlea and capsular ligament of elbow. 

1. Tuberosity on inner front side of large metacarpus. 
A. Extends the leg. 

Extensor Metacarpa Obliauus: 

0. External border of radius. 

1. Head of inner metacarpal bone. 

A. Extend and rotate the metacarpals outward. 



22 VETEREVAKY ANATOMY, HISTOLOGY, 

Extensor Pedis: 

0. Base of epitrochlea, external lateral ligament, front of humerus and head 
of radius. 

1. Pyramidal process of os pedis. 

A. Extends the carpus, and the phalanges on each other. The tendon of 
this muscle sends a strong slip to the extensor suffraginis; receives a band 
from the suspensory' ligament on each side in front of the os suffraginis, and 
is attached to the front of all the phalanges. 

Extensor Suffraginis: 

0. Ei'xternal lateral ligament, side of ulna, head and shaft of radius. 

1. Head of os suffraginis. 
A. To extend the digit. 

Its tendon receives a band from the extensor pedis and a check ligament 
rising from the trapezium. 

6. Posterior Anti-Brachial Group: 

Flexor Metacarpi Externus: 

O. Summit of the epitrochlea of humerus. 

I. By one tendon to the head of the outer splint bone, another to the 
trapezium. 

A. Flex the leg and carpus. 

Flexor Metacarpi Mediiis: 

0. By a large head from the epicondyle; and a small one from the 
olecranon process. 

1. Supero-posterior part of the trapezium. 
A. To flex the leg and carpus. 

Flexor Metacarpi Intemus: 

O. Base of epicondyle. 

I Head of the inner splint bone. 

A. Flex leg and carpus. 

Flexor Pedis Perforatiis: 

O. Summit of epitrochlea. 

i. Projecting lateral parts of os coronae. 

A. Flex carpus, fetlock and pastern; and by a check ligament supports the 
weight of the body during rest. ♦ 

Its tendon receives above the carpus the superior check ligament, a fibrous 
band rising from the infero-posterior surface of the radius. It also sends slips 
to the twro proximal phalanges. 

Flexor Pedis Perforans: 

0. From the epicondyle. ^ 

1. The semi-lunar ridge on solar aspect of os pedis. 
A. Flex carpus and all joints below. 

Its tendon receives the tendons of the accessory flexors, and the inferior 
check ligament, a strong fibrous band rising from the posterior carpal ligament. 
Ulnaris Accessorius: 

0. Posterior border and summit of olecranon. 

1. Tendon of perforans near the carpus. 
Radialis Accessorius: 

0. Posterior surface shaft of the radius. 

1. To perforans tendon. 

A. Both assist action of the perforans. 
Region of Pelvic Limb. 
1. Gluteal Group: 



PHYSIOLOGY, COMPARATIVE ANATOMY 23 

Gluteus Extcrnus: 

0. By one head from the anterior iliac spine; another from the second and 
third sacral spines and the gluteal fascia. 

1. Trochanter minor of femur, ischial tuberosity and sacro-sciatic ligament. 
A. Abducts the thigh. 

Gluteus Maxmuis: 

0. Iliac crest, haft, dorsum and spines, sacral and sacro-sciatic ligament, 
tendinous covering the longissimus dorsl. 

1. By one tendon to the summit of the trochanter major, by another to the 
bone below the convexity. 

A. Extend the femur on the pelvis, assist in rearing. 
Gluteus Internus: 
. O. Shaft of ilium, ischiatic spine and capsular ligament of hip. 
I. A depression inner side convexity of femur. 
A. Abduct and rotate the thigh inward. 
Rectus Parvus: 

0. Brim of the acetabulum. 

1. Anterior surface of femur below the head. 
A. Tense the capsular ligament. 
Obturator Extcrnus: 

O. Lower surface ischium and pubis and obturator ligament. 
I Trochanteric fossa.. 

A. Adduct and rotate the femur outward. 
Obturator Internus: 

0. Upper border of obturator foramen. 

1. Trochanteric fossa. 

A. Rotate the femur outward. 
Pyriforjuls: 

0. Transverse processes of sacrum and iliac shaft. 

1. Trochanteric fossa. 

A. Rotate the femur outward. 
Gemellus Anticus and Posticus: 

0. Shaft of the ischium. 

1. Trochanteric fossa. 

A. Rotate the femur outward. 

2. Internal Femoral Group: 
Sartorius : 

0. Brim of pelvis and iliac fascia. 

1. Internal straight ligament of patella. 
A. Adduct and flex the femur. 

Gracilis : 

0. Inferior surface ischio-pubic symphisis. 

1. Internal straight ligament and supero-internal surface of tibia. 
A. Adduct the limb, and tense the fascia of leg. 

Pectineus: 

0. Brim and inferior surface of pubis, pubio-femoral ligament. 

1. Inner surface femur below the trochanter internus. 
A. Adduct, flex and rotate the thigh inward. 
Adductor Brcvis. 

0. Inferior surface of pubis. 

1. Shaft of femur, middle of posterior surface. 
A. Flex, adduct and rotate femur outward. 



Y 



24 VETERINARY ANATOMY, HISTOLOGY, 

Adductor Liougt's: 

0. Postero-internal part lower surface pubis. 

1. By one tendon to the middle of posterior surface of femur, anotbei 
just above the internal condyle. 

A. Adduct and rotate the femur outward. 
Adductor Magnus: 

0. Tuberosity and inferior surface of ischium, and coccygeal fascia, 

1. Inner side internal condyle of femur. 

A. Adduct and extend the thigh, when limb is fixed assist rearing. 

3. External Femoral Group: 
Ti'iceps Abductor Feniorls: 

0. One head from spine of sacrum, sacro-sciatic ligament, coccygeal fascia 
and ischial tuberosity; the other from crest of ischial tuberosity. 

1. One tendon to the patella and its external ligament; one to the tibiaS 
crest and fascia, a third to the middle of posterior surface of femur. 

A. Extends the femur, abducts the limb. Flexes stifle joint. 

4. Anterior Femoral Group: 
Tensor Fasciae Latae: 

0. Anterior iliac spine. 

1. To the external fascia of the thigh. 

A. Flex the femur, raise the limb and tense the fascia. 
Rectus Femoris: 

0. Two depressions in iliac shaft before the acteabulum. 

1. Upper border of patella. 

A. Flex the femur and extend the leg. 
Vastus Externus: 

0. Antero-external aspect of femur from base of great trochanter downwar*. 

1. Upper and outer border of patella. 
A. Extend the leg. 

Vastus Intemus: 

0. Antero-internal surface of femur. 

1. Upper internal border of patella. 
A. Extend the leg. 

Cmreus : 

0. Lower third anterior surface of femur. 

1. Upper surface of patella and capsular ligament. 
A. Tense capsular ligament. 

5. Posterior Femoral Group: 
Biceps Rotator Tibialis. 

0. One head from spines of sacrum and sacro-sciatic ligament, another from 
the ischial tuberosity. 

1. Crest and supero-anterior part of tibia. 

A. Ebctend the femur, flex and rotate the leg outward. 
Ischio - Fenioralis : 

0. Inferior surface of ischium in front of tuberosity. 

1. Middle of posterior surface of femur. 
A. Extend and adduct the femur. 

6. Anterior Tibial Group: 
V Flexor Metatarsi: 

O. Tendinous head from a depression between the trochlea and external 
condyle of femur; fleshy head from the tendinous, and the head and groove of 
tibia. 



PHYSIOLOGY, C03IPARATIVE ANATOMY 25 

I. Tendinous part to the cuboid and great metatarsal; the fleshy part to 
the cuneiform parvumi and great metatarsal. 
A. Flex the metatarsus on the tarsus. 
EJxt elisor Pedis: 

0. Fossa between trochlea and external condyle of femur. 

1. Pyramidal process of os pedis, and front of two upper phalanges. 

A. Flex the tarsus and extend the digit. Its tendon receives those of the 
peroneus and extensor brevis, its attachments are same as in pectoral limb. 
Peroiieus : 

O. Fibula and external lateral ligament of stifle. 
Extensor Pedis Brevis: 

0. Infero-anterior part of astragalus and cuneiform bones. 

1. Both are attached to tendon of extensor pedis. 
A. Assist the extensor pedis. 

7. Posterior Tibial Group: 
Gastrocneiiiius Externus : 

0. One head from ridge above external condyle; another from internal 
condyle and posterior surface above inter-condyloid fossa. 

1. Posterior part summit of olecranon. 
A. E.'xtend the tarsus. 

Plantaris : 

0. Head of fibula. 

1. Point of OS calcis. 
A. Same as last. 
Flexor Pedis Perforatus: 

0. Supra-condyloid fossa.. 

1. Sides of OS corona. 

A. Extend the tarsus, flex the fetlock and pastern. Its tendon forms a cap 
over point of os calcis, and is attached to its sides. 
Flexor Pedis Perforans: 

0. Posterior surface and head of tibia, fibula and fibulo-tibial ligament. 

1. Semilunar ridge on solar surface os pedis" 

A. Extend the tarsus and flex the phalanges. Its tendon receives tne 
flexor accessorius, and also the check ligament, a strong fibrous band rising 
from the lower tarsal bones and metatarsal. 

Flexor Pedis Accessorius: 

0. External tuberosity of tibia. 

1. Tendon of perforans. 
A. Assist perforans. 
Popliteus : 

0. Fossa in external condyle of femur. 

1. Super-posterior surface and border of tibia, capsular ligament. 
A. Flexes and rotates leg inward, tenses capsular ligament. 
liaryngeal Group. Intrinsic Muscles: 

Ci'ico-Tliyix)ideiis : 

0. External surface of cricoid cartilage. 

1. Posterior border of thyroid. 

A. Elongate and tense the vocal cords. 
Crico-Arytenoideus Posticus: 

0. Cavity on posterior surface of cricoid. 

1. Posterior tubercle of arytenoid. 
A. Separate the vocal cords: 



26 VETERINARY ANATOMY, lUSTOLOGY, 

Crlco-Arytenoideus liateralis: 

0. Side of anterior border of cricoid. 

1. Outer tubercle at base of arytenoid. 
A. Approximate the vocal cords. 

Til yro - Ai*5'tenoideus : 

0. Inner surface angle of thyroid. 

1. Antero-external surface and border of arytenoids. 
A. Shorten and relax vocal cords. 
Arytenoidciis : 

O. and I. Across posterior surfaces of both arytenoids. 
A. Constrict the glottis. 
Extrinsic Muscles. 
Hyo-Tliyroideus : 

0. Inferior border heel process of hyoid. 

1. External side of wing of thyroid. 

A. Depress the hyoid and elevate «the larynx. 
Hyo -Eiiiglottideus : 

0. Middle of body of hyo'd. 

1. Infero-anterior surface of epiglottis. 
A. Draw epiglottis forward. 

aiUSCLES OF THE EYE. 

Retractor : 

0. Border of optic foramen. 

1. Circumference of posterior surface of sclerotic . 
A. Retracts the eye. 

Superior Rectus: 

O. Margin of optic foramen. 

A. Turns eye upward. 

Inferior Rectus: 

O. Margin of optic foramen. 

A. Turns eye downward. 

Internal Rectus: 

O. Margin of optic foramen. 

A. Turns eye inwards. 

External Rectus: 

O. Margin of optic foramen. 

A. Turns eye outward. 

The four recti are attached to the sclerotic near anterior boraer. 

Superior Oblique: 

O. Inner side of optic foramen, its tendon passing through a loop at 
base of orbital process of frontal turns outward to be inserted to the sclerotic 
between superior and external recti. 

A. Turns eye upward and inward. 

Inferior Oblique: 

0. Margin of lachrymal fossa. 

1. Infero-external surface of sclerotic. 
A. Turns eye inward and downward. 

n. mSTOIiOGY OF MUSCLE. 

Muscle tissue is a contractile structure, derived from the mesoblast. It 
contracts in one direction only, undifferentiated protoplasm countracting in all 



PHYSIOLOGY, OOan'AKATIVE ANATOMY 27 



directions. Two kinds of muscle fibers exist; striated, found in the voluntary 
muscles, their nerves coming from the cerebro-spinal system; and plain or non- 
striated found in the wall? of the digestive, respiratory, circulatory, and glan- 
dular organs, their nerves coming from the sympathetic system. 

Striated: — Each striated fiber consists of a transparent membrane (sar- 
colemma) enclosing protoplasm in which are fine firbils and a semi-fluid inter- 
fibrillar substance (.sarcoplasm) and muscle nuclei. Each fibril consists of 
alternating darker segments (transverse disc of Brucker) and lighter segment 
(incem-ediate discs of Krause) the latter divided by a dark line (Krause's mem- 
brane), the former divided by a light line (median disc of Hensen), in this 
disc is a thin membrane, the membrane of M. Heidenhain. These segments so 
grouped divide the fiber into sections called sarcomeres. The fibrils constitute 
the contractile part of the muscle fiber, and are grouped into small bundles called 
the muscle columns of Kolliker; the darker segments falling in the same plane 
giving the fiber the striated appearance. The sarcoplasm penetrates between 
the fibrils separating them from each other and from the sarcolemma, and is 
more abundant between the columns. In a cross section the muscle columns 
appear as darker areas (Conheims fields) separated by a network of sarcoplasm. 
The nuclei are sometimes imbedded in the sarcoplasm, in other cases placed 
immediately beneath the sarcolemma. Striated fibers are usually pointed at 
the ends, but are rounded where they attach to tendons, and bi-anched In 
muscles terminating under epithelium, as in the tongue and skin muscles of 
the face. Each fiber is surrounded by a thin connective tissue envelope, the 
endomysium, which binds them into primary and secondary muscle fasciculi; 
these are surrounded by a denser sheath the perimysium,, the muscle being 
made up of numerous fasciculi bound together by a still thicker membrane, the 
epimysium. 

Heart muscle is striated but involuntary, consisting of contractile primitive 
fibrils, which are grouped into muscle columns, between which there is found 
undifferentiated protoplasm, the sarcoplasm. The primitive fibrils present the 
same structure as voluntary muscle, each sarcomere consisting of the same 
grouped segments. The fibers are surrounded by a sarcolemma not as well 
developed as in voluntary muscle. The fiber does not present the regular form 
of individual cells as in voluntary muscle, but is rather a complex plexus of 
branching and anastomosing fibers which differ in size and shape. The nuclei 
are round or oval, placed near the center of the fibers, surrounded by a core 
of protoplasm in which are basic staining granules, pigment granules and fat 
droplets. 

Non-Striated: 

The fibers of plain muscle are spindle-shaped cells with round or oval 
nuclei placed in the thicker central portion. The outer part of the Uber 
consists of coarse fibrils, giving it a longitudinal striation, the central part 
being of fine anastomosing, branching fibrils. The sarcoplasm penetrates be- 
tween the fibrils, being granular at the poles of the nuclei. The cells are encased 
in a fine membrane (not sarcolemma) which forms fusiform spaces in which the 
cells lie. The plain muscle fibers of the iris and sweat glands is developed from 
the epiblast, all other plain fibers from the mesoblast. 

Development of Muscle: 

Striated fibers are developed from the mesoblast by differentiated segments 
called myotomes, in which round or oval cells appear called myoblasts which 
elongate, the nuclei proliferating without division of the cell body, or as 
observed by some investigators the fiber is developed by fusion of a number of 



2« VETEKINAKY ANATOMY, HISTOLOGY, 



myoblasts, the cell body presenting a uniform structure, the fibrills and 
striate appearing later. 

Heart muscle-tissue is developed from the mesoblast, the cells are united by 
branches of protoplasm which enlarge as development proceeds, the inter- 
spaces betvi^een the cells becoming smaller, forming a syncytium througli 
which nuclei are scattered. In this protoplasm are developed the contractile 
fibers, long, and at first of uniform structure, the segments forming the 
sarcomeres appearing later. The fibers are surrounded by delicate connective 
tissue sheaths as are voluntary muscle fibers. 

Development of non-striated muscle fiber is but little understood. The 
nuclei elongate, become rod shaped with oval ends, the cells become spindle 
shaped and stain more deeply than the surrounding cells of the mesoblast. 

ni. PHYSIOLOGY OF MUSCtiE. 
Clieiulstry of Muscle: 

1. Water 7 5 per cent. 

2. Ash .03 per cent; consisting of potassium, sodium, calcium, magnesium, 
iron, phosporic and hydrochloric acids. 

3. Organic matter 21 per cent. Soluble proteids are myosinogen, para- 
miyosinogen, myoglobulin; insoluble proteid is myostromin. The two first 
have the property of clotting, forming myosin, this process occurring after 
death is the cause of rigor mortis. The fibrous tissue yields collagen. 

4. Carbohydrates are glucose and glycogen. 

5. Fat in small quantities. 

6. Inosite, a benzene compound. 

7. Sarco-lactic acid. 

8. Extractives, creatinin and guanidin. 

9. Color, varies according to the amount of hemoglobin and muscle pigments 
called myohaematins. 

Physical Characters of Muscle: 

1. It is translucent in life becoming more opaque after death. 

2. It is extensile and elastic. 

These properties keep muscle stretched between their points of attachment, 
enabling a contracting muscle to act at once without jerks, the elasticity 
returning the parts to the resting position. Extensibility enables a muscle to 
contract without strong opposition from the opposing group, also steadying 
the motion of parts. The tension of muscle is largely due to nervous control, 
as when the nerve supply is lost a muscle becomes soft and flabby. 

3. Heat production in muscle is due to the chemical changes during 
the constant decomposition and reconstruction of muscle tissue; 

4. Electrical conditions. Resting muscle is iso-electric, but if part of a 
muscle is injured a current flows from the uninjured to the injured part; this 
is the current of injury. This property makes electrical experiments difficult, 
as the injury caused by exposing a muscle sets up this current; the heart 
muscle being the only one available. Contracting muscle generates a current 
which flows from the contracting to the uncontracting part. 

Contraction of Muscle. Voluntary Muscle: 

Muscle can be caused to contract by many forms of stimuli; electrical 
currents are usually employed In experimental work. A certain intensity of 
stimulus is required before contraction begins, this is called the minimum 
stimulus. The force of contractions increases in proportion to the increase of 
the stimulus up to a certain point after which the increase in force of con- 



PHYSIOLOGY, C03IPARATI\Ti: ANATOMY 29 

tractions does not follow increase of stimulus; this point is called the maximum 
stimulus. Each contraction is followed by a period of relaxation, but if a 
series of stimuli be applied rapidly, the periods of relaxation being shortened, 
the contractions are not uniform; this is "incomplete tetanus." If the stimuli 
are applied so rapidly that relaxation is entirely cut out there results a con- 
tinuous contraction; this is "complete tetanus." 

Mode of Action of Muscles: 

The sketletal muscles are arranged so as to act on each joint in opposing 
sets, and named flexors, extensors, adductors or abductors according to action. 
They move one part of the skeleton on another or the body from place to place 
by pulling on the bony frame work. The co-operative antagonism of groups of 
muscles is indispensible. If the extensors of a joint are paralysed the flexors 
cannot act, the guiding power of the extensors being necessary. 

Chemical Changes in Muscle During Action: 

The reaction of resting muscle is alkaline, muscle contracting out of the 
body becomes acid from the sarcolactic acid formed, this acid formed in the 
body is neutralized by the alkaline lymph. Carbon dioxide, nitrogenous ex- 
tractives and sarcolactic acid are increased during contraction; glycogen is 
decreased. Blood passing through muscle gains carbon dioxide, and sarcolactic 
acid; loses oxygen, fat and glucose. Eighty per cent of the energy expended 
in work is derived from the fats and carbohydrates the rest from the proteids, 
when an ordinary diet is given, the proteids being used principally in construction 
and repair. But if an exclusive proteid diet is given the energy can be 
derived from it. 

Contraction of Involuntary nmscle. 

This differs from voluntary muscle in important respects. They are in 
continuous slight tonic contraction, which may be increased or diminished 
by the action of nerves, yet is largely independent of them. They have a 
spontaneous regular rhythmic contraction and relaxation. Increase in the in- 
tensity of stimulus does not increase the force of the contraction, the minimum 
stimulus causing the maximum contraction. A series of stimuli do not cause 
a tentanus, but simply increase in the rapidity and force of the individual con- 
tractions. Muscles arranged around a hollow viscera contract in a regular 
rhythmic wave, starting at one end and traveling along the group of muscle 
fibers; this is the peristaltic wave and moves the contents of the tube forward. 

Heart muscle resembles other visceral muscle physiologically, but its period 
of contraction is shorter and its rhythm more rapid. 

Death of Muscle. 

This is not simultaneous with death of the individual; the muscles remain 
alive and contract under stimulation, but gradually lose their irritability and 
are then dead. 

The first necrobiotic change is rigor mortis; a disintegrative chemical 
change setting free carbon dioxide and sarcolactic acid, myosinogen changes to 
myosin, the muscles become contracted, less elastic, less extensile, and more 
opaque. Heat is evolved and the muscles become warmer. The time of onset and 
the duration of rigor mortis varies, but soon passes off and the muscles become 
soft. 



30 VETERINARY ANATOMY, HISTOLOGY, 

CHAPTER IV. 

ANATOMY OF HEART AND BLiOODVESSELS. 

Heart: — The heart is a hollow organ of striated, involuntary muscle tissue. 
It is about 8 inches long, 7 inches deep and 6 wide and weighs 6% pounds. Con- 
ical jin shape, it lies in the middle mediastinum, base upward, apex downward, 
•backward and to the left, covered by the 3rd, 4th, 5th and 6th ribs, the apex albove 
the last sternal segment. It is divided longitudinally into a right and left side by 
a complete septum; transversely into an upper auricular and a lower ventricular 
part by an incomplete septum. The septa are marked externally by deep grooves 
in which the cardiac blood vessels are lodged. Each side is divided into an upper 
chamber, the auricle, and a lower, the ventricle, the auriculo-ventricular opening 
in the transverse septum allowing the blood to pass downward, its return being 
prevented by the tricuspid valves in the right side, and by the bicuspid in the left. 
Within the right auricle we find the musculi pectinati, fossa ovalis, and foramina 
Thebesii; opening into it the anterior and posterior vena cava, coronary sinus, and 
venae cordis minmae. Through these vessels the blood is returned from the tissue 
to the right auricle. In the right ventricle are muscular columns, the carnae cal- 
umnae, and musculi papillares; the chordae tendineae attaching these to the tri- 
cuspid valves, which guard the opening into the auricle. The hlood flows into the 
ventricle through the auriculo-ventricular opening, and leaves it by the pulmonary 
artery closed by semilunar valves. After circulating through the lungs it returns 
to the left auricle by the pulmonary veins. This chamber resembles the right, 
but its walls are smoother; passing through the auriculo-ventricular opening the 
blood enters the left ventricle, which resembles the right, but with all parts 
thicker and stronger; and leaves it by the common aorta, its return being pre- 
vented by the semilunar valves. The chambers are lined by a serous membrane, 
the endocardium, which is continuous with the inner coat of the blood vessels. 
Externally it is covered by the visceral layer of the pericardium, a serous mem- 
brane, the parietal layer lining the pericardial sac, a fibrous chamber in which 
the heart lies, and by which the heart and great blood vessels are attached to the 
vertebrae above, the sternum below. 

Arteries: — Are the vessels by which blood is carried from the heart to the 
tissues. They are composed of three coats; the inner is a single layer of flat endo- 
tlielial cells attached to a layer of elastic fibers; the middle coat is' circular fibers 
of plain muscle mixed with elastic fibers; the external coat is white and yellow 
elastic fibers mixed. The coats vary in thickness in arteries of different sizes. 
The sheath of arteries is a layer of areolar tissue surrounding the artery to which 
it is loosely attached, allowing free motion, and firmly attached to the surrounding 
tissues, giving firm support. 

Tlie Cii'ciilation : — 1. Systemic; 2. Pulmonary. 

1. The systemic or general circulation carries the blood to the tissues and 
returns it to the heart by the veins. 

Coinnion Aorta: — Is the vessel by which the blood leaves the left ventricle ;i 
its branches are: 1. The coronary arteries given off in the sinuses of Valsalva, 
between the semilunar valves and the aortic wall. 

2. The anterior and posterior aorta. 
Anterior Aorta: — Branches are: 

1. Twigs to the pericardium and mediastinum, terminals are 

2. Brachials. 



PHYSIOLOGY, COJIPARATIVE ANATOMY 31 

Bracliial Arteries: — Are right and left. The right gives off the common 
carotid, the following branches coming from both alike: 

1. Dorsal; through the second intercostal space to the withers and the muscles 
of that region; in the thorax the dorsal gives off the sub-costal, which passes back- 
ward, giving off the 2nd, 3rd and 4th intercostals. 

2. Superior cervical; through the first intercostal space, passing upward on 
the ligamentum nuchae to the 2nd cervical vertebra; to the muscles of the upper 
cervical region, anastomosing with the dorsal and vertebral; in the thorax it gives 
off the first intercostal. 

3. The vertebral; passing out between the first ribs, under tlie transverse 
process of the seventh cervical, through .the foramen in the sixth to the second 
inosculating with the ramus anastomoticus of the occipital; to the lateral cervical 
muscles and by the intervertebral foramina to the spinal cord and its membranes. 

4. Internal thoracic; downward to the second bone of the sternum, backward 
to the ensiform cartilage, terminating in the anterior abdominal, which anas- 
tomoses in the rectus muscle with the epigastric; and the asternal, which anas- 
tomoses with the intercostal in the thirteenth space. 

5. Inferior cervical; ascending and descending branches, to muscles and 
glands of lower cervical region. 

6. External thoracic; around the first rib backward to the pectoral region. 

7. Prescapular; to the shoulder and muscles of the dorsum of scapula. 

8. Subscapular; passes up the posterior border of scapula to the angle, gives off 
the nutrient scapular, and posterior circumflex to the internal scapular and 
posterior bra^^chial groups of muscles. 

Tlie humeral artery is the continuation of the brachial. Descends on the 
inner side of the humerus to the point of the elbow; it's branches are: 

1. Anterior circumflex, passes between the heads of the coraco-brachi'alis to 
the shoulder and anterior brachial muscles. 

2. Profunda humeralis; to the caput, humeralis obliquus, and extensors. 

3. Ulnar; under the scapulo-ulnaris down the back of the limb to the knee, 
inosculating with the recurrent of the posterior radial to form the superior carpal 
arch. 

4. Coraco-radial; to the muscle of the same name. 

5. Apterior radial; down the anterior surface of the elbow to the fore arm, 
to the -flexor muscles and carpus. b-/.tl. . .„ err 

Tlie posterior radial is the continuation of the humeral, it's branches are: 

1. Interosseous, through the radio-ulnar arch down radio-ulnar groove 
forming a plexus above the carpus with the anterior radial, and giving off the 
nutrient radial and branches to the elbow and flexor muscles. 

2. Recurrent radial, passes outward and downward, under the flexor 
metacarpi medius. inosculates with the ulnar to form the superior carpal arch, 
from which a branch descends in the annular ligament inosculating with the small 
metacarpal below the carpus to form the inferior carpal arch. 

3. Small metacarpal, passes down behind the annular ligament on the inner 
and posterior side of the knee; crosses to the outer side of the leg, inosculates 
with a branch from the superior carpal arch to form the inferior carpal arch, from 
which spring four branches; two anterior interosseous palmers which pass round 
the heads of the splint bones, down the inter-metacarpal grooves, anastomosing 
with the anterior radial above and a branch of the large metacarpal below; and 
two posterior interosseous palmers which pass down the sides of the suspensory 
ligament, inosculating above the fetlock with ascending branches of the large 



32 VETERINARY ANATOMY, HISTOLOGY, 

metacarpal, forming' the sessamoidean arch. The posterior radial also gives 
branches to the elbow and posterior antibrachial group of muscles. 

The large inetaicai"pal is the continuation of the posterior radial. It passes 
down beneath the posterior annular ligament, to the inner side of the flexor 
tendons with a vein and nerve; above the fetlock it gives off a branch which 
divides and ascends to inosculate with the posterior interosseous palmers to form 
the sessamoidean arch from which arises the inner and outer digitals, which may 
be regarded as the continuation of the great metacarpal. 

The digital arteries rising from the sessamoidean arch, are the continuation 
of the great metacarpal. Passing outward and downward over sides of the digit, 
with a vein in front and a nerve behind, inside the lateral cartilages to the 
plantar foramina, entering them as the plantar ungual arteries; branches of 
the digitals are: 

1. Perpendicular, on sides of os suffraginis, downward and forward, in- 
osculates with it's fellow to form the superficial coronary arch which sends 
twenty branches to the coronary ligament. 

2. Transverse, divides under the lateral cartilage, one branch between the os 
corona and the extensor tendon with its fellow forms the deep coronary arch; 
ti second branch inosculates with it's fellows above the navicular bone. 

3. Artery of the frog; behind the pastern .ioint, to the lateral cartilages and 
.sensitive frog. 

4. Preplantar ungual; through the preplantar fissure, groove and foramen, 
where it enters the substance of the os' pedis to anastomose with the circulus 
arteriosis; at it's origin it sends a retrograde branch to the bulb of the frog at the 
foramen a second retrograde to the external side of the lateral cartilage. 

The Plantar unguals are the continuation of the digitals. Entering the 
plantar foramina they inosculate to form the circulus arteriosis, within the bone; 
from this spring the anterior laminals which ascend through foramina in the wall 
to the sensitive laminae. Fourteen branches, the inferior communicating pass 
through foramina above the edge of the wall, uniting to form the circumflex 
artery which runs around the toe, from which ascending branches rise to the 
sensitive laminae, and fourteen descending branches, the solar arteries to the 
sensitive sole, uniting posteriorly to form the inferior circumflex. 

The common carotid is given off by the right brachial, passes forward, 
leaves the thorax between the first ribs, dividing at this point into right and 
left carotids. 

The right and left carotids pass up the infero-lateral aspect of the neck; 
the vagus, recurrent laryngeal and sympathetic nerves being enclosed in the 
same sheath with the artery. At the level of the larynx it divides into occipital, 
internal and external carotid. 

Before dividing it's branches are: muscular, tracheal, and oesphageal twigs; 
the thyroid to me thyroid gland; and the thyro-laryngeal to the thyroid body and 
the larynx. 

The Occipital: — Passes upward to the external anterior foramen in the 
wing of the atlas, terminating on it's upper surface in the cerebro-spinal and 
musculo-occipital. The cerebro-spinal enters the neural canal by the internal 
atloid foramen, dividing on the inferior surface of the cord into a posterior branch 
which unites with its fellow to form the middle spinal; and an anterior branch 
which unites with it's fellow to form the basilar, which passes forward; it's 
branches are. 



PHYSIOLOGY, COMPARATIVE ANATOMY 33 

Basilar: — 1. Twigs to the medulla and pons varolii. 2. Posterior cerebellars 
3. Anterior cerebellars. 4. Posterior cerebrals, forming the posterior boundary 
of the circle of Willis, inosculating with the posterior communicating of the 
internal carotid. 

Musculo -occipital divides into an ascending branch to the occipital region 
and a descending branch to the superior cervical region. 

Occipital Branches are: 

1. Prevertebral which divides into muscular branches to the anterior straight 
muscles and articulation, and a meningeal branch which divides into a superior 
entering the cranium by the condyloid foramen, and an inferior by the foramen 
lacerum basis cranii. 

2. Mastoid to the temporal muscle, and by the parieto-temporal conduit to 
the dura mater. 

3. Ramus anastomoticus, under the wing of the atlas backward through 
the posterior foramen, inosculating with the vertebral, forms collateral circulation 
between carotid and vertebral arteries. 

External carotid; the continuation of the carotid, passes upward between 
((jha guttural pouch and the parotid gland, between tne hyoid cornu and the 
hyoideus magnus to the neck of the condyle of the inferior maxilla, where it 
divides into the internal maxillary and the superficial temporal; the latter gives 
off the anterior auricular to the temporal and anterior muscles of the ear and the 
concha, and the subzygomatic, which divides into the transverse facial and 
masseter. 

Branches of the External Carotid: 

1. Glosso-facial, given off below the hyoid cornu passes forward, turns 
upward over the border of the lower jaw in front of the masseter muscle, termin- 
ating above the maxillary spine in the dorsal nasal and angular artery of the 
eye. Branches of the glosso-facial are: 1. Pharyngeal, to the velum palati and 
pharynx. 2. Lingual to the tongue. 3. Sublingual to the sublingual gland and 
extrinsic muscles of ■ the tongue, 4. Inferior labial to the lower lip. 5. Superior 
labial to the upper lip. 6. Lateral nasal to side of nose. 

2. Maxillo-muscular is given off above the hyoid cornu, divides into the 
pterygoid, to the pterygoid muscles, and posterior masseter to the masseter muscle. 

3. Posterior auricular, passes to the back of the base of the ear, to the 
muscles and skin of the region, and to the cartilages. 

The internal maxillary is the continuation of the external carotid; passing 
between the neck of the lower jaw and the hyoid cornu, through the pterygoid 
foramen, across the floor of the orbit into the maxillary hiatus, and enters the 
palatine conduit as the palatine artery. 

Branches of the Internal Maxillary are: 

1. Inferior dental, through the pterygoid muscles to the inferior dental 
foramen and canal emerging on the external surface of the inferior maxilla at 
the mental foramen; to the teeth, gums and the lower lip. 

2. Pterygoid fasciculus, to the pterygoid muscles. 

3. Tympanic, to the walls of the tympanum. 

4. Great meningeal, by the foramen lacerum basis cranii to the dura mater. 

5. Posterior deep temporal, upward to the temporal muscle, anastomosing 
with the masseter by a branch passing through the sigmoid notch. 

6. Anterior deep temporal, to the temporal and attolentes muscles. 

7. Ophthalmic; given off in the pterygoid foramen; by the orbital hiatus to the 
orbital fossa, by the internal orbital foramen to the cranial cavity where it 



34 VETERINARY ANATOMY, lUSTOLOGY, 

divides into meningeal branches to tlie falx cerebri and dura mater, anastomosing 
with it's fellow and the anterior cerebral arteries; and the internal lateral nasal 
which passes through the cribriform plates to the ethmoid volutes and septum 
nasi. In the orbital fossa the ophthalmic gives off muscular branches to the 
muscles of the eye; the ciliary arteries to the choroid coat, ciliary process and 
iris; the arteria centralis retinae which passes through the axis of the optic nerve; 
the supra orbital through the supraorbital foramen to the skin and muscles of 
the frontal region; the lachrymal to the larchrymal gland and upper eye lid; and 
cranial branches to the anterior lobe of the cerebrum. 

8. Buccal; to the fatty cushion of the orbit, muscles and molar glands. 

9. Staphyline; through the staphyline groove to the soft palate. 

10. Superior dental; by the superior dental foramen and canal, emerging 
at the infra-orbital foramen, to teeth, cheek and lachrymal sac. 

11. Spheno-palatine to the nasal chambers by the spheno-palatine foramen. 
The Palatine: — Continuation of the internal maxillary, by the paltine 

foramen and groove to the incisive foramen where it inosculates with its fellow, 
giving off the palato-labial which rises through the incisive foramen to the 
upper lip and gums. 

The internal carotid; given off at the carotid trifurcation passes upward 
and forward to the cranial cavity by the foramen lacerum basis cranii to the 
cavernous sinus where it is joined to it's fellow by a transverse branch, pierces the 
dura rnater at the fissure of Sylvius, it divides, one branch again dividing into 
the anterior cerebrals which pass forward, uniting in the longitudinal fissure, 
forming the anterior and antero-lateral boundaries of the circle of Willis, and 
the middle cerebrals which pass to the fissure of Sylvius and the inferior and 
lateral region of the cerebrum. Another branch, the posterior communicating 
passes backward by the side of the inter-peduncular space, inosculating with 
the posterior cerebral of the basilar, forming the lateral boundary of the circle 
gf Willis, 

The posterior aorta rises from the common aorta at the -level of the fourth 
•dorsal vertebra, passes upward, backward and to the left of the sixth or seventh 
'dorsal, through the aortic hiatus, under the bodies of the vertebrae to the last 
lumbar, where it terminates in the aortic quadrifurcation; two internal and two 
external iliacs. 

Visceral Branches of the Posterior Aorta are: — 

1. Broncho-oesophageal; bronchial to the lungs, the nutrient blood, terrnin- 
jiting in the pulmonary capillaries; oesophageal to the oesophagus and posterior 
mediastinum. 

2. Coeliac axis; it's branches are: (1) Gastric, which divides" into right, to 
the oesophagus and anterior aspect of the greater cul-de-sac; and left, to the 
posterior aspect of the lesser cul-de-sac. (2) Splenic; passes to the left over the 
fundus of the stomach, enters the hilus of the spleen, passing to it's apex where 
it becomes the left gastro-epiploic, along the greater curvature of the stomach 
to the lesser cul-de-sac, anastomosing with the right gastro-epiploic of the hepatic. 
(3) The hepatic; passes to the right, enters the transverse fissure of the liver, 
dividing into three series of vessels; the rami vasculares to the walls of the bile 
ducts and blood vessels; the rami capsulares to the capsule; and the rami lobulares 
to the substance of the lobules. The hepatic gives off the right gastro-epiploic to 
the greater curvature of the stomach anastomosing with the left gastro-epiploic 
of the splenic; the duodenal, passing along the curvature of the duodenum 
anastomoses with a branch of the great mesenteric. 



PHYSIOLOGY, COMPARATIVE ANATOMY 35 

3. Great mesenteric; which divides into (1) Left, consisting of twenty or 
more branches to the small intestines. (2) Right, which divides into the ileo- 
caecal to the ileum; the superior caecal to the upper, the inferior caecal to the 
lower, fissure of the caecum; and gives off the artery of the arch; right colic 
to the first and second portions of the large colon. (3) Anterior; which 
divides into the left colic, to the third and fourth portions of the great colon; 
a branch to the pancreas, and the artery of the floating colon. 

4. Lesser mesenteric artery breaks up into thirteen or more branches to the 
floating colon and rectum; the last five forming no arches are called the 

haemorrhoidal arteries. 

5. Renal, right and left, to the kidneys, an anterior branch going to the 
suprarenal capsule. 

6. Spermatic, through the inguinal canal, down the spermatic cord to the 
testicle. These in the female are the utero-ovarian, which pass in the folds of 
the broad ligament to the ovaries and horns of the uterus. 

7. Sinall testicular to ureters, vas deferns, peritoneum, and cord. This in the 
female is the uterine, to the body and horns of the uterus. 

Parietal Branches of the Posterior Aorta are: — 

1. Aortic intercostals, thirteen in number, pass to the upper part of the 
intercostal spaces where they divide into a superior branch, the dorso-spinal, to 
the skin, dorsal muscles, and by the inter-vertebral foramina, to the spinal cord 
and it's coverings; and an inferior, intercostal branch to the thoracic and inter- 
costal muscles and pleura. 

2. Lumbar arteries, five or six pairs, are distributed like the intercostals to 
the" spinal cord, and skin and muscles of the region. 

3. Phrenic, given off the aorta near the diaphragm, to the crus of the 
diaphragm. 

4. Middle sacral, a small branch continuing the aorta in the middle line is 
rudimentary in the horse, frequently absent. 

The Internal Iliacs: — Are the terminal branches of the posterior aorta; ex 
tending from the last lumbar vertebra to the ilio-pectineal eminence; their 
oranches are: — 

1. The umbilical; a large artery in the foetus, is but a fibrous cord in the 
adult. 

2. The Internal Pudic; passing backward and downward, over the ischial 
arch to the bulb and crura of the penis; its branches are: (1) Twigs to Cowper's 
gland. (2) The vesico-prostatic, to the prostate gland, vesicula seminalis, and 
bladder.' (3) The perineal, to the anus and urethral muscles. In the female the 
internal pudic supplies the rectum, vulva, vagina and bladder; the vesico-prostatic 
becoming the vaginal artery. 

3. The ilio-lumbar; to the sacro-iliac articulation, sublumbar, and gluteus 
maximus muscles. 

4. The iliaco-:^emoral; to the crural triceps and tensor fasciae latae. 

5. The obturator; passes backward and downward, through the obturator 
foramen; it gives branches to the ischio-fibial muscles, and terminates in the 
cavernous, to the dorsum; and the crural, to the bulb and crus of the penis. 

6. The gluteal; through the great sciatic notch, to the gluteal muscles. 

7. The lateral sacral; passes backward along the side of the sacrum, sending 
the sacro-spinal branches through the inferior foramina, to the spinal cord; 
terminating in the ischiatic, to the ischio-tibial muscles; and the lateral coccygeal, 
to the tail; the middle coccygeal is usually given off the left lateral sacral. 



36 VETERIlSrARY ANATOMY, HISTOLfOGY, 

The external iliacs are given off the aorta at the level of the last lumbar 
vertebra; their branches are: — 

1. The circumflex ilii, passes to the anterior iliac spine where it divides, an 
anterior branch to the transversalis and the internal oblique; and a posterior to 
the iliacus, internal oblique and tensor fasciae latae. 

The femoral artery is the continuation of the external iliac; it's branches 
are: — ■ 

1. Prepubian, passing to the back of the internal abdominal ring; it divides 
into epigastric, which runs forward to the abdominal muscles; and the external 
pudic, passing down the inguinal canal to the dorsum of the penis and the 
scrotum. The external pudic gives off the subcutaneous abdominal, to the skin, 
sheath, and superficial inguinal glands. In the female the dorsal artery of the 
penis becomes the mammary, to the substance of the gland. 

2. Profunda femoris, to the hip joint, posterior and external femoral muscles. 

3. Superficialis femoris, to the internal and anterior femoral muscles. 

4. Small muscular; to the stifle joint, nutrient of the femur, and to muscles 
surrounding the femur. 

5. Saphenic, passes to the inner surface of the thigh, down to upper aspect of 
tarsus where it forms an anastomotic arch with the posterior tibial and femoro- 
popliteal. 

Tlie popUteal is the continuation of the femoral; from the heads of the 
gastrocnemius to the upper part of the tibia, where it divides into the anterior 
and posterior tibial. It's branches are: — 

1. Femoro-popliteal, to the skin and muscles at the back of the haunch. 

2. Articular branches to the stifle joint. 

3. Muscular branches to the posterior aspect of thigh lower down. 

4. Posterior tibial, down side of leg to point of os calcis where it forms with 
the saphenic, the tarsal arch; from this arch arise two recurrent branches to 
anastomose with branches of popliteal; two small branches, the internal and ex- 
ternal plantars, pass down the sides of the deep flexor tendon anastomosing with 
the preforating pedal, forming the inferior tarsal arch; from this arch two small 
branches run to the flexor tendons; and an internal and external interosseous 
plantar pass down the borders of the flexor tendons to the fetlock joint, anas- 
tomosing with the great metatarsal to form the sessamoidean arch. 

The anterior tibial is the continuation of the popliteal, passes forward through 
the tibio-fibular arch to the anterior surface of the tibia, outward across the 
front of the hock, becoming the great metatarsal; it's branches are: — 

1. The peroneal to the muscle of that name. 

2. The perforating pedal passing backward in a canal between the cuboid 
and cuneiform bones down the back of the hock to form the inferior tarsal arch. 

Tlie great metatarsal is the continuation of the anterior tibial, passes down 
the groove between the large and external small metatarsal bones, under the 
nodule on the distal end of the latter, through the bifurcation of the suspensory 
ligament, anastomosing with the plantar branches of the posterior tibial to form 
the sessamoidean arch. 

The digital arteries spring from this arch, their distribution being the same 
as in the front limb. 

Pulmonary system, consists of the right side of the heart, pulmonary arteries 
capillaries and veins. The blood returned from the body by the veins of the 
systemic system enters the right auricle, passes to the right ventricle through the 
aurlculo-ventricular opening, it's return being prevented by the tri-cuspid valves. 



PHYSIOLOGY, C05IPARA1IVE ANATOMY 37 

It leaves the right ventricle by the pulmonary artery, which rises from the 
summit of a conical prolongation, the conus ateriosis. The return of the blood 
is here prevented by the semi-lunar valves. 

Tlie pulomonary artery curves upward and backward to the upper part of 
the left auricle, where it divides into a right and left branch, which enter the lungs 
with the bronchi, breaking up and passing to the lobules of the lung tissue, 
forming a dense network of capillaries over the walls of the air cells. From 
these capillaries the pulmonary veins rise, uniting to form larger veins, leaving 
the lung at the root by four large vessels, two from each lung, which enter 
the left auricle. These veins are destitute of valves, and carry arterial blood, 
while the pulmonary artery carries venous blood. 

Veins: — Are the vessels by which the blood is returned to the heart after 
passing through the capillaries; they resemble arteries in structure, but are 
lighter in all their coats, and are, with some exceptions, provided with valves 
which prevent a return flow and assist the onward movement of the blood. 

Coronary veins return the blood from the heart muscle, are distributed as 
satellites of the arteries, and unite to form one large vein which enters the right 
auricle by the coronary sinus; numerous minute veins entering by the foramina 
Thebesii. 

Bronchial veins return the blood from the lung substance, entering the cor- 
onary vein at the sinus. 

The portal system consists of the veins from the digestive tract and spleen; 
the anterior and posterior mesenteric and gastro-splenic veins, which unite 
to form the portal; this enters the liver at the transverse fissure, reaching the 
interlobular connective tissue as minute branches, the interlobular veins, which 
enter the lobule as capillaries; these are collected in the center of the lobule 
to form the intralobular vein, which empties into the sublobular; these unite to 
form large trunks which reach the anterior fissure of the liver and empty into 
tlie posterior vena cava. The capillaries of the hepatic artery also unite with these 
veins, which are called the hepatic veins. 

Renal veins, right and left return the blood from the kidneys, entering the 
posterior vena cava. 

Spermatic veins returning blood from the testicles, are in the female the 
utero- ovarian, to the vena cava. 

Phrenic A'eins from the diaphragm to posterior vena cava. 

Digital veins, formed by the union of the deep and superficial coronary 
plexuses and veins of the frog, unite between the flexor tendons and suspensory 
ligament to form the sessamoidean arch. The coronary plexuses receive blood 
from the solar, laminal and interosseous veins. 

Metatarsal A-eins, internal, external and deep rise from the sessamoidean 
arch; the two first unite to form the saphenic, the deep going to the anterior 
tibial, which with the posterior tibial forms the popliteal, it being continued 
as the 

Femoral, which is a satelite of the femoral artery, having the same branches 
and also the saphena, which enters it about the middle. 

Tlie external iliac continues the femoral in like manner. 

Tlie internal iliacs are satelites of the arteries, and uniting with the external 
forms the posterior vena cava, which passes through the anterior fissure of the 
liver, the foramen dextrum of the diaphragm, and a notch in the right lung 
enters the right auricle. 

Metacarpal A^eins, internal, external and deep rise as do the metatarsals; 



38 VETERINARY ANATOMY, HISTOIX)GY, 

the internal is continued as the subcutaneous, which divides to form the basilic 
which terminates in the humeral, and the cephalic, emptying into the jugular. 

The external and deep unite to form the posterior radial which g-oes to the 
humeral. The external subcutaneous enters the cephalic. The spur vein, froni 
the flank enters the humeral. 

The humeral is a satelite of the artery, and is continued as the brachial. 

The jugular originates by two branches, the superficial temporal and in- 
ternal maxillary, receiving blood from the cranial cavity by the parieto-temporal, 
subsphenoidal, and alveolar veins; and from the head by satelites of the arteries. 

Vena azygos, receiving blood from the spinal, and psoe muscles, the thirtee» 
posterior right and six posterior left, intercostals and the oesophageal veins, enters 
the anterior vena cava. 

The anterior vena cava is formed by the union of the brachials and jugulars 
and receives the internal thoracic, vertebral, superior cervical and dorsal and 
vena azgos; emptying into the right auricle. 

II. HISTOLOGY OF THE HEART AND BLOOD VESSELS. 

Heart: — The heart consists of three distinct coats, the endocardium, myocar- 
dium, and pericardium. 

1. The endocardium is a single layer of flat endothelial cells, resting on a thin 
membrane of plain muscle, connective tissue, and elastic fibers; this membrane 
rests on a thick, loose layer of elastic tissue firmly attached to the myocardium. 
Between these layers are found traces of the fibers of Purkinje absent in man, 
but well developed in some of the lower animals. These fibers are large, clear, 
quadrilateral cells, with granular protoplasm, numerous nuclei and striated 
margins. 

The auriculo-ventricular valves are a duplication of the endocardium, muscle 
fibers beneath the auricular layer, and connective tissue fibers beneath the ven- 
tricular layer. The semilunar valves are of the same structure, elastic fibers being 
liensely arranged in the nodules. 

2. The myocardium consists of muscle fibers (see histology of muscles) ; 
between the fibers and bundles of fibers is a layer of connective tissue containing a 
dense network of blood capillaries. The muscle of the auricles consists of an 
external layer common to both sides, and an inner layer, the fibers of which do 
not extend from one auricle to the other. The muscle of the ventricles consists of 
a superficial layer rising from the auriculo-ventricular ring, winding round the 
septum to end in the tendon of the papillary muscle of the opposite ventricle; 
the deep layer also rising in the auricula-ventricular ring winds around to the 
septum, crosses over backward or forward in it, to end in the same way in the 
opposite ventricle. 

The auriculo-ventricular ring consists of connective tissue and elastic fibers, 
and almost completely separates the muscle of the auricle from that of the 
ventricle. 

S. The pericardium consists of a visceral layer, the epicardium, firmly at- 
tached to the myocardium, and a parietal layer, the pericardium, attached to 
a thick layer of connective tissue which forms a supporting \vall externally. Be- 
tween the visceral and parietal layers is the pericardial cavity, containing a small 
quantity of fluid. These layers consist of a connective tissue stroma, covered by 
flat mesothelial cells. 

The heart is freely supplied with blood vessels ramifying in the connecMve 



PHYSIOLOGY, CO»£PAKATIVE ANATOMY 39 

tissue which send one or more capillaries to each fiber; the endocardium and 
auriculo-ventricular valves receive blood in the same manner; the semilunar valves 
are non-vascular. » 

The veins of Thebesius, which open freely into all chambers of the heart, 
communicate with the coronary arteries by capillaries, and with the veins by 
larger vessels; by this means no area of the muscle is deprived of blood even 
though that from the coronary artery direct is cut off. 

Lymphatic networks exist in the endo and peri-cardium, but their pres- 
ence in the myocardium has not been fully demonstrated. 

Heart Nerves: — Nerves of heart consist of sympathetic neurones under the 
pericardium whose cell bodies are grouped to form ganglia, and whose neuraxes 
form intricate pleuses, from which fine fibers go to terminate on the muscle 
fibers. The cell bodies are surrounded by end-baskets, the telodendria of medul- 
lated fibers which reach the heart through the vagi. The changes in action pro- 
duced by stimulation of the vagi are due to altered activity in these sympathetic 
cells. Further nerve supply reaches the heart through sympathetic neurones 
whose cell bodies are situated in the inferior cervical and stellate ganglia, but 
whose mode of ending has not been fully determined. The cell bodies of these 
nerves are surrounded by end-baskets of telodendria of medullated nerves which 
leave the cord by the inferior roots of the anterior dorsal nerves. This combina- 
tion supplies the augmentor impulses to the heart. Other sympathetic nerves 
(the exact location of whose cell bodies is uncertain) from plexuses in the walls 
,0'f the coronary arteries, terminating in the media; these are the vasomotor 
nerves. Sensory nerves, after forming- plexuses, lose their medullated sheath; 
the telodendria, which vary greatly in shape, terminate in the endocardium, 
pericardium, and walls of the blood vessels of the heart; their terminations being 
surrounded by granular protoplasm and branched connective tissue cells. 

Arteries: — ^Consist of three coats; the inner, (intima) is a single layer of 
endo-thelial cells, a subendothelial layer of connective tissue fibers, limited ex- 
ternally by the fenestrated membrane of Henle. The middle coat (media) con- 
sists of plain muscle fibers in circular form, separated from each other by con- 
nective tissue and elastic fibers, limited externally by the external elastic mem- 
brane. The external coat (adventitia) consists of connective tissue and elastic 
fibers. The comparative thickness of the different coats varies greatly in arteries 
of different caliber. 

Veins: — The inner coat of veins consists of three layers; internally a single 
layer of endothelial cells, then a layer of muscle cells and connective tissue, and a 
third of fibrous connective tissue, limited externally by the internal elastic layer. 
The middle coat is not well developed, rarely consisting of a complete muscular 
layer, frequently only of isolated fibers. The external coat has an inner 
longitudinal layer of muscle fibers, and externally one of white fibrous and a few 
elastic fibers. "Valves of veins are a duplication of the intima. 

Capillaries consist of a single layer of endothelial cells, and connect the 
arterial and venous pre-capillary vessels. 

Sinusoids are irregular spaces in the parenchyma of organs, consisting of a 
single layer of endothelial cells; and are found in the liver, supra renal, heart, 
parathyroid, carotid gland, and hemolymph glands. 

Retia. niirabilia; consist of the breaking up of certain small vessels into 
capillary or precapillary vessels, and after a short course again uniting to form 
a larger vessel, later forming true capillaries. 

Sinuses are large spaces lined by endothelial cells; surrounded by connective 



40 VETERINARY ANATOMY, HISTOLOGY, 

tissue and capable of great distension, (except in cranial sinuses) when the ef- 
ferent vessels are constricted by pressure or otherwise. 

Direct coniinunication of arteries and veins occurs in certain exposed areas 
of skin; (ear, tip of nose, toes) also in the meninges and kidneys. 

Nerves of blood vessels are plexuses of sympathetic nerve fibers in the ad- 
ventitia from which fine fibers extend to terminate on the muscle cells of the 
media. These are the vasomotor nerves, and control the caliber of the vessels. 
Sensory nerves are also found in the adventitia, and in large vessels in the media. 

m. HISTOIX3GY OF THE BLOOD. 

Blood: — In early fetal life masses of cells from the mesenchyme, called 
blood islands, appear in the area vasculosa. In the center of the mass free cells 
are seen, which are the first blood cells of the embryo, entering the circulation by 
blood channels formed by the confluence of the blood islands, the cells surround- 
ing the first blood cells going to form the primitive vascular walls. 

At this period the cells are all nucleated and proliferate in the capillaries 
and blood spaces of the liver. The white cells appear later; their early origin 
is uncertain, but in late fetal, and adult life they are formed by the spleen and 
lymphatic glands; at this period the red blood cells are formed by spleen and 
red bone marrow. 

Blood of adult life consists of a fluid coagulable substance, the blood plasma, 
or intercellular substance, in which the formed elements are suspended. Th(^ 
formed elements are: — 

1. Red blood corpuscles called erythrocytes, non-nucleated, biconcave, cir- 
cular dies, transparent, pale yellowish red, elastic, with rounded edges and 
smooth surfaces, without a true cell membrane. The cell consists of protoplasm 
holding in solution a blood pigment called hemoglobin; a complex proteid com- 
posed of a globulin and a pigment, hematin, which combines with hydrochloric 
acid to form hemin, or Teichmann's crystals. 

2. White blood corpuscles, large, nucleated cells, having several centrosomes 
grouped to form a microcenter, about which the fibrillar structure of the 
protoplasm is arranged radially. The meshes of the net work are filled with a 
niore fluid substance and contain the specific granules of the cell. The white 
corpuscles vary in size and structure and present the following varieties: 

1. Small and large lymphocytes. 

2. Mononuclear leucocytes. 

3. Transitional leucocytes. 

4. Polymorphonuclear or polynuclear leucocytes. 

About twenty per cent of the white cells are of the first variety; two to four 
per cent of second and third and seventy per cent of the fourth. They are again 
divided into several varieties, according to the size, staining qualities, etc., of the 
granules. White cells are devoid of hemoglobin, have amoeboid movement and 
the power of creeping through capillary walls (diapedesis) ; taking up and 
digesting or removing foreign matter, germs, etc. 

3. Blood platelets, hematohlasts, or thrombocytes, are minute delicate cells, 
round or oval, without hemoglobin, having amoeboid movement; with short 
thread-like processes which are passed out from the cell and drawn in again. 
When removed from the body they break up quickly with formation of fibrin 
and coagulation of the blood. 



PHYSIOLOGY, COaiPAKATIVE ANATOMY 41 

IV. PHYSIOLOGY OF HEART AND BLOOD VESSELS. 

Heart: — By alternate contractions and dilatations the heart receives the blood 
from the veins, discharges it into the arteries, forces it through the capillaries, and 
by the veins back to the heart. 

A cardiac cycle is the series of changes which occur in the heart during one 
complete contraction and dilatation, and a period of rest, called the pause. It 
includes: First, the auricular systole (contraction); second, the ventricular systole, 
and auricular diastole (dilatation); third, combined auricular and ventricular 
diastole, or pause. 

The time occupied by one cycle is in the horse, 1 1-2 seconds, divided as fol- 
'llo'ws: A. S., 3-16; V. S., 9-16; A. D. and V. D. combined, 12-16. The entire A. 
D. is 21-16, (9-16 during V. S. and 12-16 combined D.). The entire V. D. is 15-16, 
(3-16 during A. S. and 12-16 combined D.). 

Sounds Pi'oduced by Action of Heart are:— 

1. The first sound, during the V. S'., is longer and softer than the second, and 
is caused by the contracting muscle walls, and closing auriclo-ventricular valves. 

2. The second sound, shorter, harder and louder, occurs at the beginning of 
the V. D. and is caused by closing of the semilunar valves in the aorta and 
pulmonary artery. 

Apex beat, so called, occurs over a small area over the anterior wall of the 
left ventricle, and is caused by the hardening of the heart muscle, and a partial 
turn of the heart against the chest wall. 

Valve action; the auriculo-ventricular valves lying flat against the inner 
ventricular wall during the pause, are moved inward and upward by the whirl 
of blood descending into the ventricle when the A. S. occurs; being held at a 
certain point by the chordae tendinae, the V. S. forcing the blood upward, com- 
pletes the closure by pressing the edges and a part of the surface together; thus 
the blood is prevented from re-entering the auricles from below. When V. S. 
ends and V. D. begins these valves drop again to the position of rest, and so remain 
until the next A. S. begins. 

The semilunar valves, unlike the A. V. valves, remain closed except during 
the V. S. and are opened only when the pressure in the ventricles exceeds that in 
the arteries, when their leaflets are forced against the arterial walls, closing 
promptly again the instant V. D. begins. 

The cardiac arteries, unlike others, are filled during the V. D., their openings 
being between the semilunar valves and the aortic wall are closed during V. S. 
when these valves are pressed back. 

Arteries receive the blood from the ventricles during V. S., the elastic walls 
are distended by the blood forced into them, and recoiling when V. D. occurs, 
the pressure of blood flowing into the capillaries is kept constant. A further 
control of blood pressure is accomplished by the muscular coat of the smaller 
arteries, by changing the size of the lumen, the amount of blood going to any part 
of the body is regulated according to the needs of that part. 

CapUlaries receive the blood from the arteries; through their walls the fluid 
part of the blood passes, delivering to the tissues nutritive material received 
from the digestive tract, and oxygen received in the lungs; and receives from 
the tissues waste material and carbon dioxide. 

Veins receive the blood from the capillaries, and conduct it to the heart, 
emptying impure venous blood into the right auricle by the anterior and posterior 
vena cava and coronary sinus; and purified arterial blood into the left auricle 
by the pulmonary veins. 



42 VETERINARY ANATOMY, HISTOLOGY, 

Blood pressui-e is the pressure on the blood in the vessels by the action of 
the heart, elastic arterial walls, and the resistance of the arterioles and capil- 
laries — called peripheral resistance. 

The pressure varies, being- greatest in the aorta, decreasing with the distance 
from the heart, and the increase in the number of vessels through which it 
passes, being low in the capillaries, yet lower in the veins, and as they approach 
the heart the pressure is negative during A. D. Changes in pressure caused by 
respiration are: a marked rise as inspiration becomes full; and a marked fall 
as expiration becomes full. 

The pulse is a wave of expansion passing through the blood and over the 
arterial walls at each V. S. Three conditions are present to cause the impulse: 
1. A- fluid forced into the vessels in jets. 2. At the point of outflow an obstruc- 
tion to the stream leaving the vessels. 3. Elastic walled vessels which expand 
as each jet is forced into them, recoiling again between jets. One or more of 
these conditions being absent in capillaries and veins, there is no pulse found in 
them. 

Nerves supplying the heart are derived from both the cerebro-spinal and 
sympathetic systems, (see histology of the heart). 

1. The superior cardiac branch of the vagus; section of it causes no change, 
stimulation of peripheral end no change, stimulation of central end causes a 
slowing of the heart by reflex action through the inferior cardiac branch of the 
vagus, (inhibitory nerve); and a marked fall in blood pressure by reflex action 
through the splanchnic nerves, which are vaso-dilators to the vessels of the 
abdomen. On account of the action it is called the depressor nerve. 

2. The inferior cardiac branch of the vagus; section causes acceleration of 
heart action, showing that this nerve is always in action, and that it is inhibitory, 
■which is further proven by stimulating the peripheral end when slowinff of 
action follows. 

3. Sympathetic fibers from the inferior cervical and stellate glanglia; section 
of these causes no change; stimulation of the peripheral end increases force and 
rate of heart; these are the augmentor and accelerator nerves. 

4. Intracardiac nerves are fully described in histology of heart. 
Nerves Supplying the Blood Vessels are: — 

1. Vaso-constrictors; derived from the sympathetic, they reach the vessels 
in company with other nerves, ending in the muscle fibers; section causes dila- 
tation of the vessel. 

2. Vaso-dilators; pass out by the inferior roots of the spinal nerves, do not 
pass through sympathetic ganglia, but run as medullated fibers to their terminal 
ganglia. 

Vasomotor centers presiding over these nerves are: 

1. A vaso-constrictor center in the pons varolii and medulla oblongata. Re- 
moval of this center causes dilatation of the arterioles, showing that it is con- 
stantly in action, maintaining a tonic contraction of the vessels. Stimulation 
causes general contraction. 

2. A vaso-dilator center, which seems to be distributed through the medulla 
and spinal cord. Removal causes no change, showing that it is not constantly 
in action, but only when stimulated. This center is not general in action like 
the vaso-constrictor, but acts in relation to different parts of the body, in 
response to stimulation received from such part. 

Blood is the medium through which the tissues receive nutriment, and dis- 
pose of waste matter. 

Color: — Arterial blood is bright red, due to presence of larger per cent, of 



PHYSIOLOGY, COMPARATIVE ANATOMY 43 

oxygen; venous blood is dark red or purplish, due to less oxygen and more 
carbon dioxide. 

Specific Gravity: — Horse, ox, and pig, 1060; sheep, 1050-8; dog, 1050. 

Reaction, alkaline, due to sodium phosphate and bicarbonate. 

Taste, saline due to sodium chloride. 

Composition of Blood: 

I*i'Oteids: — Plasma contains in solution, proteids; serum albumin, serum 
globulin, and fibrinogen. 

Extractives: — Flats, cholesterin, lecithin, creatin, urea, hippuric acid, uric acid 
and grape sugar. 

3Iineral Matter: — Sodium chloride, carbonate and phosphate, potassium 
chloride, and phosphate, and phosphates of calcium and magnesium. The red 
cells contain iron and hemoglobin, and in varying amount the mineral matter 
mentioned is found in both red and white. 

Gases: — ^Arterial blood contains, oxygen, 20 per cent.; carbon dioxide, 40 per 
cent.; nitrogen, 2 per cent. 

Venous blood contains, oxygen, 12 per cent.; carbon dioxide, 45 per cent.; 
nitrogen, 2 per cent. 

Oxygen is held in weak chemical combination with the hemoglobin of the 
red corpuscles. 

Carbon dioxide is held in weak cheinical combination with the sodium salts 
in the plasma. 

Niti*ogen is simply absorbed by the plasma and does not vary in amount. 

Clotting: — In the living vessel the fibrinogen is in soluble form; but when 
blood is removed from the vessel, or coines in contact with broken walls or 
foreign matter, the fibrinogen changes to insoluble fibrin and a soluble globulin 
which remaihs in solution. This change is caused by a ferment called thrombin, 
which is formed by the action of a calcium salt on a nucleo-proteid called pro- 
thrombin, shed out from the blood platelets and white corpuscles. The insoluble 
fibrin forms in the blood in the form of small fibers crossing each other in all 
directions, enclosing the corpuscles in the meshes. The clot is at first a jelly- 
like mass, but by contraction of the fibrin the fluid is squeezed out and appears 
as a clear straw-colored fluid; this is called serum, and differs from plasma only 
In having the fibrin removed and the ferment added. The fibrin and corpuscles 
remain a solid mass, the clot. 

Hemoglobin, the coloring matter of blood is contained in the red cells; is 
a proteid, but is crystalizable; forms a weak chemical combination with oxygen, 
called oiy-hemoglobin. 

Metlienioglobin is a stronger combination of it with oxygen, and can be 
produced by the action of acids or alkalies on oxy-hemoglobin. Carbonic oxide 
Hemoglobin is a strong chemical combination of carbonic oxide with hemoglobin, 
and is formed in the blood during carbonic oxide poisoning. 

Hematin is the iron carrying part of hemoglobin. When acted on by hydro- 
chloric acid hematin yields hemin. 

Hematoporphyrin is hematin from which the iron has been reinoved. 

Hematoidin is an iron free coloring matter derived from hematin, and is 
chemically identical with bilirubin, the coloring matter of bile. 

Changes in the blood during circulation. 

1. In the lungs; the capillaries of the pulmonary system are spread over the 
walls of the air cells, and as the venous blood passes through tliem the hemo^ 
globin absorbs oxygen from -the air, and the plasma discharges carbonic acid 



44 VETERINARY ANATOMY, HISTOLOGY, 

Into the air, contained in the air cells. This change is brought about by the 
difference of pressure of these g-ases in the blood and in the air. 

2. In the tissues the opposite change takes place; the oxygen is transferred 
to the tissues, and carbonic acid is absorbed by the plasma and uniting with 
the sodium salts, is carried to the lungs and discharged into the air. 

The waste material produced by the life processes is also taken up by tfte 
»/ood and carried to the excretory organs for removal. 

Functions of the Plasma: — A fluid medium by which the formed elements, 
nutritive material and mineral matter, are carried to the tissues. And carbonic 
acid and waste material removed. 

runctions of the Red Coriniscles: — Chiefly as 'a carrier of iron and hemo- 
globin, whereby oxygen is taken up and carried to the tissues. 

Functions of the White Ck>rpuscles: — They remove or destroy broken down 
tissue cells, foreign matter and injurious germs. Assist in causing coagulation, 
and in repair of injured tissues. 

Function of tlie blood platelets appears to be an active part in the coagula- 
tion of the blood. 



CHAPTER V. 



ANATOMY OF THE L.Y3IPHATIC SYSTEM. 

The lymphatic system begins as spaces or clefts between the elements of the 
tissues, uniting to form larger vessels which pass through one or more groups 
of glands, all terminating in two large vessels, the thoracic duct which receives 
the lymph from all the vessels of the body except the right pectoral limb, and 
right side of the head, neck, and thorax. 

The thoracic duct. 

Begins in the lumar region, between the aorta and vena cava, by a dilatation 
called the receptaculum chyli, passes forward on the right side of the vertebrae, 
enters the thorax by the aortic hiatus; at the 6th dorsal vertebra turns down- 
ward over the base of the heart and to the left, terminating in the jugular con- 
fluent, by a dilated orifice guarded by a valve. 

The lymphatic vein. 

At the junction of the jugular veins of the right side, and emptying into the 
confluent, is guarded by a valve and receives the vessels of the right pectoral 
limb, and right side of the head, neck and thorax. 

Glands. 

Are placed on the course of the lymph vessels, singly or in groups, all ves- 
sels passing through one or more before entering the large vessels. 

The system is divided into regions and groups. 

The posterior region. 

Includes the pelvic limbs, pelvic walls and organs, and abdominal walls. The 
following groups of glands receive the vessels of this region. 

Siiblumbar. 

In the angles of the iliac arteries and aorta, their efferent vessels going to 
the receptaculum chyli. They receive vessels from the deep inguinal and iliac 
glands, and branches from the pelvis, rectum, double colon and spermatic cord. 



PHYSIOLOGY, COMPARATIVE ANATOMY 45 

Deep inguinal. 

Under the crural arch, on the inner aspect of the crural vessels, passing- for- 
ward to the pubis, receiving vessels from the superficial inguinal glands, and 
popliteal group. 

Superficial inguinal. 

In front of the inguinal ring at the side of the sheath, their efferent vessels 
pass up the inguinal canal to the deep inguinal. 
Popliteal. 

Between the adductor magnus and biceps rotator tibialis, near the femoro- 
popliteal artery, receive vessels from the limb and thigh. 

Iliac. 

In the bifurcation of the circumflex ilii artery, receive the efferents of the 
precrural glands. 

Precrural. 

On the antero-internal border of the tensor fascia lata, receive vessels from 
the anterior and inner parts of the thigh. 
Abdonial viscera region. 

Kectimi and floating colon; large colon; caecum; small intestine; stomach. 

The glands of thes>' organs are usually arranged in chains following the 
curvatures of the viscus, and along the arteries, with numerous small glands 
on the lymphatic vessels in the messentary. 

Spleen. 

Are deep, in the parenchyma, and superficial, on the surface. 

liver. 

Arranged as in the spleen. 

Thoracic viscera. 

A group of small glands in the posterior mediastinum. The bronchial glands 
in the angle of bifurcation of the trachea, extending into the lungs and along the 
lower surfacd of the trachea. 

Thoracic walls. 

A double chain of small glands above the pleura, close to the centra of the 
vertebrae; a large mass on the ziphoid cartilage behind the heart. 

Anterior region. 

Pi'epectoral. 

On each side of the jugular confluents, passing into the thorax under the 
brachial vessels; receiving the efferent vessels from the brachial, prescapular, 
submaxillary and guttural groups. 

Guttural. 

On the lateral wall of the pharynx from the guttural pouch to the thyroid 
gland. 

SiibniaxilUiry. 

At the base of the tongue, between the digastric and mylo-hyoid muscles. 

Prescapular. 

On the internal surface of the levator humeri, just above the cariniform 
cartilage. 

Brachial. 

Tv/o groups; one on the inner surface of the internal condyle, the other on 
the inner surface of the upper third of the humerus. 

Ijacteals, 

The lymph vessels in the villi of the intestines by which the products of fat 
digestion are taken up. For description see histology of digestive system. 



46 VETERINARY ANATOIVIY, HISTOLOGY, 

n. HISTOIiOGY OF THE LYMPHATIC SYSTEM. 

Lymphoid tissue, nodules, and glands. Hemolymph glands. Marrowlymph 
glands. Lymph vessels. 
Lyniplioid tissue. 

Consists of fine fibrils of connective tissue and cells (endoplasm and nuclei) 
placed in the fibrils, often at nodal points. Within the meshes of the reticulum 
formed by these fibrils lymph cells are densely arranged. Lymphoid tissue may 
be diffuse, or In well defined round masses or nodules. 
Notliiles. 

Are single, solitary lymph follicles; or gathered into groups, agminated 
lymph-nodules. They are scattered in the mucous membrane of the digestive or- 
gans. At the periphery of the nodule the cells are arranged concentrically; in 
the center the meshes are larger, the cells less densely packed and show active 
mitosis, the newly formed cells being pushed toward the periphery and swept into 
the circulation by the lymph current which circulates through the meshes; the 
central area is the germ center, or secondary nodule. 

Glands. 

Are of more complicated structure than the podules. Kidney or bean 
shaped, with a depression called the hilum, and enclosed in a capsule consisting 
of an outer loose and an inner more compact, layer of connective tissue wtth 
elastic fibers and muscle cells. The inner layer sends processes into the sub- 
stance of the gland dividing it into imperfectly separated compartments. The 
lymphoid tissue of the glands consists of nodules which form a peripheral layer 
between the septa, (cortical nodules) from which cords of lymphoid tissue 
(medullary cords) extend toward the center; the cords and nodules are sur- 
rounded by a layer of loose, wide-meshed lymphatic tissue which lies between 
them and the capsule and trabeculae, the surface next to the nodules and cords 
being lined by endothelial cells, forming the lymph-sinuses of the gland. 

Afferent vessels enter the gland by piercing the capsule on the convex sur- 
face, the efferent vessels leaving at the hilum. 

The lymph flowing into the gland passes through the sinuses, surrounds the 
nodules and cords, and passing into the terminal sinus at the hilum flows out by 
the efferent vessels, taking with it the newly formed lymph cells. 

Arteries entering at the hilum form capillaries in the nodules and cords; 
these unite to form veins which leave the gland at the hilum. The blood and 
lymph vessels in ordinary lymphatic glands have no direct communication with 
each other. 

Medullated and nonmedullated nerve fibers enter the gland with the blood- 
vessels, on which they terminate. 

Hemolymph glands. 

Are much like typical lymph glands in structure; having a capsule, trabe- 
culae and sinuses; the arteries enter at the hilum and communicate with the 
sinuses through capillaries. 

The lymphoid tissue is divided by the sinuses into anastomosing masses, con- 
sisting of an adenoid reticulum in which red and white blood-cells are found. 

In the reticulum and blood-«inuses are found all varieties of leucocytes, and 
mononuclear phagocytes which contain disintegrating red blood cells and pig- 
ment granules. 

Hemolymph glands have no afferent or efferent lymph vessels. 

Marrow lymph -glands. 

Differ somewhat in structure and variety of leucocytes from those described. 



PHYSIOLOGY, COMPARATIVE ANATOMY 47 

Lymphatic vessels. 

Begin as clefts or intercellular spaces in the organs and tissues; uniting- to 
form capillaries which resemble blood capillaries in structure, usually larger; 
these unite to form veins, thin walled, and having numerous valves, which give 
thein a knotted appearance. The veins finally terminate in two large vessels 
which empty into the blood stream at the jugular confluent. 

Lacteals. 

See histology of digestive system. 

ni. FUNCTIONS OF THE LYMPHATICS. 

Vessels. 

The blood plasma passes through the capillary walls into spaces in the 
organs and tissues. From these spaces the tissue cells select the substances re- 
quired in their life processes, and discharge into these same spaces the 
waste formed during cell action. From these spaces the lymphatic capillaries 
originate, forming veins which finally reach the blood stream in the large 
veins near the heart. As the vessels pass through the lymph glands the different 
forms of corpuscles developed there are added to the fluid flowing through them. 

From the digestive organs the chyle absorbed by the lacteals is also added 
to the flowing lymph, passing through the thoracic duct. 

IV. ANATOMY, HISTOLOGY AND PHYSIOLOGY OF THE SPLEEN. 

Anatomy. 

The spleen is a reddish-grey, ductless gland, placed on the left of the greater 
curvature of the stomach, from which the gastro-splenic omer\tuni passes to its 
anterior border. It weighs, in the horse, from two to four pounds; has a base 
lying near the left kidney, the apex directed downward and forward; its upper 
surface contacts the diaphragm, its lower the large colon; its posterior border 
is convex and thin, its anterior concave and thick, and marked by the hilum, a 
depression at which the bloodvessels and nerves enter. It is covered by periton- 
eum, under which is a fibrous capsule. 

Histology. 

The capsule consists of connective tissue, elastic fibers and plain muscle 
cells; sending processes into the organ which form a framework in which the 
vessels are imbedded. The frame-work breaks up to form a reticular tissue 
which supports the spleen substance. Between and surrounding the trabeculae 
IS a tissue rich in cells, blood-corpuscles and blood-vessels, called the spleen pulp. 
This is divided into lobules, each divided by intralobular trabeculae into about 
ten compartments, in which the spleen pulp is arranged in anastoinosing columns 
called pulp cords. 

At the hilum, both arteries and veins are enveloped in a fibrous sheath from 
the capsule, which is continued over the veins throughout their course, but soon 
leaves the arteries. After losing the fibrous sheath the adventitia of the arteries 
changes to lymphoid tissue; this forms nodules (Malpighian corpuscles) on the 
arteries having the reticular tissue, germ centers, etc., of typical lymphoid no- 
dules; the newly formed (lymphocytes are pushed out into the channels of the 
spleen lobules. 

After passing through the Malpighian corpuscles the arteries lose their 
lymphoid sheath, regain the adventitia (which is continued over the capillaries) 
Dreak up Into fine arterioles which pass through the center of the spleen lobule 
sending a branch to each compartinent. These branches divide to form capll- 



48 VETERINARY ANATOMY, mSTOLOGY, 

laries which course in the pulp cords, ending in small expansions, the ampullae of 
Thoma, having side openings which communicate with the pulp spaces. From 
these pulp spaces the venous capillaries rise, unite to formi veins which finally 
leave the organ at the hilum. 

In the reticulum of the spleen pulp the following cells are found: 

1. Nucleated red blood-cells in small numbers. 

2. Fully developed red blood-cells. 

3. Giant cells. 

4. Ijarge cells containing red blood-corpuscles, or their remains, with or 
without pigment. 

5. The different varieties of white blood cells. 

The Ijlood flowing through the ampullae of Thoma enters the pulp-spaces, 
from these into the veins, carrying with it the cells found in the spaces. 
Physiology. Functions of the spleen. 

1. Formation of white blood-corpuscles. 

2. Formation of red blood-corpuscles. In the fetus, and after severe hemorr- 
hage and in certain diseased conditions in the adult. 

3. Disintegration of red blood-cells. This is not complete, no hemoglobin 
being found free in the blood of the solenic veins. 

4. Acts as a reservoir for blood in case of plethora of other abdominal vis- 
cera. 

5. The presence of large amount of urea and other nitrogenous products in 
the spleen point to an active part in nitrogenous metabolism. 



CHAPTER VI. 

ANATOMY OF THE NERVOUS SYSTEM. 

The nervous system of the horse consists of the brain, spinal cord, mem- 
branes covering them, smaller nerve centers called ganglia, found on the course 
of nerve trunks, 12 pairs of cranial nerves, 42 or 43 pairs of spinal nerves, and the 
sympathetic chain and its branches. It is divided into two systems, the cerebro- 
spinal and sympathetic. 

The oei'ebro-spinal system consists of the brain, spinal cord, their mem- 
branes and nerve trunks, and certain small nerve centers called ganglia. 

Tlie brain is that part enclosed within the cranial cavity, and has four divis- 
ions. The cerebrum, cerebellum, pons Varolii and medulla oblongata. 

The cerebrum consists of lateral halves (hemispheres) separated above by the 
longitudinal fissure, united below by the corpus callosum; it's exterior marked by 
deep fissures called sulci, which divide it into elevations called convolutions. The 
fissure of Sylvius on the lateral surface divides it into an anterior and a greater 
lobe; in a bifurcation of this fissure is a cluster of convolutions, the island of 
Reil. 

The cerebellum, or lesser brain, placed behind the cerebrum, consists of a 
body and three pairs of peduncles; the body is divided into a middle and two 
lateral lobes; the anterior part of the middle lobe is the vermiform process, to it 
is attached the valve of Vieussens, the two covering the aqueduct of Sylvius and 
the 4th ventricle. The cerebellum is grey externally, a branching mass of white 



PHYSIOLOGY, COMPARATIVE ANATOMY 49 

matter internally is the arbor vitae, and a small grey mass in the center of this 
is the corpus dentatum. 

The pons Varolii is a band of white matter extending across the inferior as- 
pect of the cerebellum, turning upward laterally to form its middle pair of pe- 
duncles; it separates the medulla from the cerebrum on the base of the brain. 

The medulla oWongata is the expanded upper part of the spinal cord, lying 
anterior to the foramen magnum, and below the cerebellum. It is divided by a 
superior and inferior median fissure, the upper expanding to form the 4th ven- 
tricle, the lower ending in the foramen caecum. On each lateral half, from the 
lower fissure upward, the small elevations are; the inferior pyramids, olivary 
bodies, restiform bodies, intermediate fasciculi, and superior pyramids. 

The lateral ventricles are cavities in the hemispheres of the cerebrum, sepa- 
rated by the septum lucidum; the 3rd ventricle is a cavity in the infero-central 
part of the brain, communicating with the lateral ventricles by the foramen of 
Monroe, and with the 4th ventricle, which lies below the cerebellum, by the 
aqueduct of Sylvius. 

On the base of the brain, the peduncles, of the cerebrum posteriorly, and the 
optic tracts and commisure anteriorly bound the inter-peduncular space, in which 
we find the pituitary gland, infundibulum, corpus albicans, locus perforatus pos- 
ticus, and pons Tarina. On each side of the optic tracts is the locus perforatus 
anticus, in front of the tract the tuber cinerium, and on the lower surface of the 
cerebrum anteriorly the olfactory bulbs. 

Meninges of the brain are: externally the dura mater, a thick white fibrous 
membrane forming the internal periosteum of the cranial bones, and supporting 
the brain by processes which pass b.etween the divisions. These are: the falx 
cerebri, in the longitudinal fissure attached anteriorly to the crista galli process, 
posteriorly to the ossific tentorium, the tentorium cerebelli, between the cere- 
brum and cerebellum, attached to the lateral ridges of the ossific tentorium; the 
falx cerebelli, between the lobes of the cerebellum, attached to the ossific tentor- 
ium and upper border of the foramen magnum. The arachnoid, the middle mem- 
brane, is a serous membrane, attached firmly to the dura mater, and loosely to 
the pia mater, forming between the layers a closed sac. The pia mater, inner 
membrane, firmly attached to the brain, dips into all depressions and passing 
into the lateral ventricles; is largely composed of blood vessels. The subarach- 
noidean space lies between this and the arachnoid. 

Tlie cranial nerves are 12 pairs, leaving the cranium by various foramina. 

1. Olfactory, by foramina in the cribriform plates of the ethmoid to the nasal 
chambers, is the nerve of the special sense of smell. 

2. Optic, by the optic foramen to the eye ball, the nerve of sight. 

3. Motores oculorum, by the foramen lacerum orbitale, to the superior, in- 
ferior, and internal recti, inferior oblique, levator palpebrae and inner half 
of retractor muscles, and branches to the lenticular ganglion; motor nerve. 

4. Pathetic; by foramen patheticum, to superior oblique. 

5. Trifacial, rises, by two roots, anterior and posterior; on the posterior root 
the Gasserian ganglion gives off (A) the ophthalmic; by the foramen lacerum 
orbitale to the orbital fossa; its branches are: a, supraorbital, through the supra- 
orbital foramen to the upper eye lid, skin and muscles of the forehead; b, lach- 
rymal, to the lachrymal gland, muscles and skin on the anterior part of ear; c, 
palpebro-nasal, branches to the membrana nictitans, lower eye lid, lachrymal sac, 
and ophthalmic ganglion; it then enters the cranial cavity by the internal orbital 
foramen, passes through the cribriform plates to the nasal chambers; sensory 
nerve; (B) Superior maxillary, by the foramen rotundum, across the orbit to the 



50 VETERINARY ANATOMY, HISTOLOGY, 

maxillary hiatus, by the dental canal to the infraorbital foramen, terminating on 
the face in three branches, to the nose, false nostril, upper lip, and muscles and 
skin of the face; sensory. Its branches are: a, to the eye lids and skin; b, palato- 
maxillary by the palatine foramen to the palate and gums; c, posterior palatine, 
to the soft palate; d, nasal, by spheno-palatine foramen to the nasal chambers 
and Meckel's ganglion; e, dental, to the molar and incisor teeth. 

(C) The inferior maxillary, unites with the anterior root of the 5th; by the 
foramen lacerum basis cranii, to the inferior dental foramen, by the canal to the 
mental foramen, as the mental nerves to the lower lip. It's branches are: a, 
masseter; b, buccal; c, internal pterygoidean; d, subzygomatic; e, lingual; f, mylo- 
hyoidean, and dental. This is a mixed nerve; the anterior branch which joins it 
being nnotor. 

6. Abducens, by the foramen lacerum orbitale to the external rectus and ex- 
ternal half of the retractor, muscles. 

7. Facial, by the internal auditory meatus, through the aqueduct of Fallopius 
to the stylo-mastoid foramen; its branches are, intraosseous; a, superficial petro- 
sal which with a sympathetic branch forms the Vidian nerve, by the Vidian canal 
to Meckels ganglion; b, lesser superficial petrosal, to the otic ganglion and the 
stapedius muscle; c, chorda tympani, to the tympanic cavity, by the stylo-mastoid 
foramen to the lingual branch of the 5th. Extra-osseous branches; a, styloid; 

b, cervical; c, anterior, middle and posterior auricular; the 7th terminates in two 
sets of branches; an inferior to the muscles of the cheek, lower jaw and lip; 
superior to the muscles of the nose and upper lip. Motor. 

8. Auditory, by the internal auditory meatus to the internal ear, nerve of 
hearing. 

9. Glosso-pharyngeal, by the foramen lacerum basis cranii, to the mucous 
membrane and substance of the tongue; its branches are: a, nerve of Jacobson, 
to the tympanum and its membrane; a branch to the superior cervical ganglion, 
carotid plexus, and vagus nerve, and to the muscles of the pharynx. 

10. Vagus (pneumogastric) by the foramen lacerum basis cranii, to tlie 
carotid sheath, along the oesophagus in the thoracic cavity, to the stomach and 
solar plexus. Its branches are: a, to the 7th; b, to the superior cervical ganglion; 

c, to the pharynx; d, superior laryngeal, by an opening in the thyroid cartilage to 
the mucous membrane and muscles; e, to the inferior cervical ganglion; f, recur- 
rent laryngeal, leaves the thorax below the trachea, passes up to the larynx, to all 
the intrinsic muscles except the crico-thyroideus; branches to the trachea and 
oesophagus; g, branches to the cardiac plexus; h, branches to the bronchial 
plexus. Terminating in an inferior branch to the stomach; and a superior to the 
solar plexus. 

11. Spinal accessory, a motor nerve, rises from the cervical portion of the 
spinal cord, runs forward between the roots of the spinal nerves, enters the cran- 
ium by the foramen magnum, receives filaments form the medulla, leaves the 
cranium by the foramen lacerum basis cranii; sends branches to the superior cer- 
vical ganglion, maxillary gland, levator huneri, sterno-maxillaris, trapezius and 
rhomboideus brevis muscles. 

12. Hypo-glossal, by the condyloid foramen, to all the muscles of the tongue, 
and branches to the first cervical nerve and superior cervical ganglion, motor. 

The spinal cord is the part of the cerebro-spinal system lodged In the neural 
canal, extending from the foramen magnum to the posterior end of the sacrum* 
tapering to a point, the conus medullaris, from which a bundle of nerves goes to 
the adjacent structures; this bundle is the cauda equina. 



PHYSIOLOGY, CX>]VIPARATIVE ANATOMY 51 

Meninges of the cord are: Externally, the dura mater, attached to the fora- 
men magnum, continuous with the dura mater of the brain, extends to the first 
bones of the coccyx, blending with their periosteum. It is separated from the 
periosteum of the neural canal by areolar tissue and a, plexus of veins, forming- a 
loose sheath to the cord, pierced opposite each inter-vertebral foramen for pas- 
sage of the spinal nerves. The middle coat, arachnoid, continuous with that of 
the brain, is attached in the same manner. The inner, pia mater, also continuous 
with that of the brain resembles it in structure and distribution. The ligamen- 
tum denticulatum is a narrow fibrous band running between the roots of the 
spinal nerves, from the foramen magnum backward; its inner border attached 
to the pia mater, its outer denticulated border attached to the dura mater between 
the openings for the nerves. 

Fissures of the cord are: A superior mediu*»-, narrow but deep, and an in- 
ferior broader and shallow, divide it into lateral columns, which are united in 
the center by an inferior white, and a superior grey commisure. Each column is 
white externally, having internally a crescent of grey matter, with a superior and 
an inferior horn, or cornu. 

The spinal nerves rise by a superior sensory root, and an inferior motor root, 
which pass through the intervertebral foramina; the inferior passing under a 
ganglion on the superior, the two unite to form a spinal nerve, which again di- 
vides into an upper and a lower branch. The upper branch supplies the muscles, 
skin and other tissues on the upper aspect of the trunk, the lower branch going 
to the same parts below the vertebral column. 

The spinal nerves are named according to the regions of the vertebral column: 
cervical, 8 pairs; dorsal, 17; lumbar, 6; sacral, 5; coccygeal, 6 or 7. 

The phrenic nerves are formed by a branch from the brachial plexus, one 
from the 6th and one from the 7th cervical nerves; enters the thorax between the 
first ribs, passes between the layers of the mediastinum to the central part of the 
diaphragm, and is distributed to it. 

The brachial plexus is formed by the inferior branches of the 7th and 8th 
cervical, the first and part of the second, dorsal nerves; these unite and pass to 
the inner side of the arm, supplying the pectoral limb. The branches are: 

1. Anterior scapular, to the dorsum of the scapula. 

2. Thoracic, six or seven branches to the muscles between the shoulder and 
trunk. 

3. Subscapular; a, a small branch to the subscapularis; b, a large branch, the 
axillary, to the teres externus and levator humeri. 

4. Radial, to the scapulo-ulnaris, caput, and extensor muscles of the fore- 
arm, and skin and elbow joint. 

5. Ulnar, to the bend of the carpus, under the annular ligament; it divides 
one branch to the skin, carpus and outer side of the metacarpus; the other unites 
with a branch of the median to form the external metacarpal nerve. 

6. Median, down the inner side of the elbow and radius to the carpus under 
the annular ligament, dividing to form the internal metacarpal, and a branch to 
the external metacarpal. Its branches are, a branch to the pectoral muscles; the 
musculo-cutaneous, to the elbow, skin and muscles of the arm and forearm. 

7. Metacarpal, internal and external, pass down the sides of the flexor ten- 
dons (anastomosing by a transverse branch) to the fetlock, where they divide 
into anterior, middle and posterior digital nerves. 

8. Digital, the anterior descends in front of the digital vein to the anterior 
of the foot; the middle, to the fetlock pad, and sole. The posterior, behind the 
digital artery to the basilar process, enters the lateral fissure, to the substance of 



52 VETEKINAKY ANATOMY, HISTOLiOGY, 

the bone and the laminae; and filaments to the flexor tendons, frog, and bone. 
The himbo-sacral plexus; an anterior division from the inferior branches of 
the last two lumbar nerves; and a posterior from the first three sacral nerves. 
Branches of the anterior division are: 

1. Iliaco-muscular, numerous small branches to the iliac muscle. 

2. Crural (anterior femoral) to the anterior and inner femoral groups; the 
internal saphenic, to the inner aspect of the limb down to the fetlock; another 
long subcutaneous branch running with the saphenic artery. 

3. Obturator, through the obturator foramen to the muscles on the inner 
aspect of the thigh. 

Branches posterior tlivision. 

1. Anterior gluteal, through the great siatic notch to the tensor fasciae latae 
and gluteal muscles. 

2. Posterior gluteal, through sciatic notch to the gluteus externus, triceps 
and biceps rotator tibialis muscles. 

3. Great sciatic, through the great sciatic notch, down the posterior face of 
the femur, to the stifle, where it gives off a short branch to the muscles of the 
posterior tibial region, and is continued as the popliteal; its branches are: a, ex- 
ternal popliteal, to the external aspect of the stifle, terminating in the anterior 
tibial, to the muscles of the region; and the musculo-cutaneous to the muscles 
and skin on the antero-external aspect of the limb down to the pastern joint; b, 
the external saphenic, to the external aspect of the tarsus and below it; c, a 
small branch to the small muscles of the gluteal group; d, the posterior crural, 
to the posterior and lateral femoral, and posterior tibial muscles. 

Popliteal is the continuation of the great sciatic; to the hock, where it divides 
into the internal and external metatarsal nerves. 

Metatarsal nerves pass down the borders of the flexor tendons to the fetlock, 
and are continued as the digitals as in the fore limb. 

The sympathetic system consists of two chains of nerves extending from the 
head to the coccyx, under the lateral aspect of the bodies of the vertebrae, and is 
described in regions. 

Cephalic portion consists of the ophthalmic, Meckels, and the otic ganglia; 
which communicate with the superior cervical ganglion. 

Cervical portion, of the superior and inferior cervical ganglia, united by an 
intermediate cord. 

Thoracic portion, from the inferior cervical ganglion to the diaphragm; of 17 
small ganglia (one opposite each intervertebral foramen) united by a cord. 

Lrtunbar portion, and sacral portion, simply continuation of the thoracic. 
Each ganglion receives a branch from the spinal nerve opposite it and sends a 
branch to the cord. From the ganglia branches are given off which form plex- 
uses; the principal ones are: 1, the gutteral; 2, cavernous; 3, carotid; 4, pharyn- 
geal; 5, tracheal; 6, solar; 7, lumbo-aortic; 8, posterior messenteric; 9, spermatic; 
10, pelvic. 

Distribution of the sympathetic system will be considered with each organ. 

n, HISTOLOGY OF THE NERVOUS SYSTEM. 

The neural canal. 

Is developed in early fetal life by a dorsal invagination of the ectoderm, and 
contains cells called neuroblasts. From these the entire nervous system is devel- 
oped, and consists of cell bodies having one or more processes, which are of two 
kinds. 



PHYSIOLOGY, COMPARATIVE ANATOMY 53 

Processes. 

1. Unbranohed, of uniform diameter, having lateral offshoots (collateral 
branches) which end in small tufts of fibrils. These branches usually form the 
central part of a nerve fiber, and are called neuraxes (neurites, neuraxones, 
axones, axis cylinder processes); they usually join the cell body by an expanded 
cone (implantation cone) fitting into a depression in the granular substance of 
the cell; more rarely tiiey rise from a dendrite. 

2. Branched processes with nodular, uneven outline, which divide into many 
fibrils which taper to end in points or small nodules, and are called dendrites; 
terminal arborizations of nerve fibers are called telodendria. 

Cells. 

Are large, nucleated, having nucleoli and fibrillar protoplasm with chromat- 
ophile granules, which are continued into the dendrites as nodular pointed rods, 
giving the dendrites a varicose outline. Cells are of two types: 

1. Cells having a loag neuraxis continued as a nerve fiber. 

2. Cells having a short neuraxis which divides to form a complicated arbor- 
ization called the neuropodia of Kolliker. 

Neurones. 

A neurone is the cell body, dendrites and neuraxis complete; very rarely has 
more than one neuraxis, and a neurone without a neuraxis has never been found 
in vertebrates. Neurones are called unipolar, bipolar or multipolar, according to 
the number of processes; present great variety in size, shape, and number of pro- 
cesses; are intermingled in different parts of the system, yet in many regions 
have fixed characteristic appearance by which their source can be determined. 
The most important of these are: 

1. Motor, in the anterion horn of the spinal cord, large multipolar neurones 
having many branching dendrites which terminate near the cell body, the neur- 
axis forming part of a nerve fiber. 

2. Large neurones in the cerebellum (Purkinje's cells), with a flask shaped 
body, from its lower portion a neuraxis with collateral branches, from its uppev 
one or two large dendrites, the smaller branches of which are dotted with 
granules. 

3. In the cerebral cortex, large neurones with pyramidal body, one large 
dendrite rising from the apex, several smaller ones from the sides and angles, 
and the neuraxis from the base or a basal dendrite. 

4. In the granular layer of the cerebellum; neurones with a small body and 
Bhort dendrites. 

5. In the spinal, and homologous cranial ganglia are grouped the cell bodies 
of sensory neurones, with large round, oval or pear shaped bodies, a single pro- 
cess which divides (T or Y shaped division of Ranvier), one branch going to the 
brain or cord, the other to the periphery. Although the central branch is re- 

- garded as the neuraxis and the other as the dendrite, they are alike in structure, 
both forming the central axis of a nerve fiber. 

6. In the sympathetic ganglia, multipolar neurones having fine chromato- 
phile granules, numerous dendrites forming plexuses of many branches in the 
ganglia; the neuraxis rising from an implantation cone, or from a dendrite. 

All nuerones develop from a single cell, functionate as a single cell, yet are 
never found disconnected, but always in close proximity to other neurones; the 
telodendrion of one neurone forming a feltwork round the cell body of one or 
more neurones (end basket), or may mingle with the telodendria of one or more 
dendrites of other neurones. By this contiguity they are linked into chains, so 
that a physiological continuity exists between them. 



54 VETERINARY ANATOaiY, HISTOLOGY, 

The dendrites transmit impulses to the cell body (cellulipetal), the neuraxes 
to the nerve endings or central organ (cellulifugal), 

Nei*ve fibers. 

The neuraxes of cells of type 1 and the dendrites of sensory neurones form 
the chief elements of all nerve fibers. They consist of axis fibrils imbedded in a 
semifluid substance, the neuroplasm, the whole surrounded by a delicate mem- 
brane the axolemma, and called an axial cord; this is surrounded by special mem- 
branes which determine the class of nerves to which they belong. 

There are two kinds of fibers. 

1. Medullated, in which the axial cord is surrounded by the medullary sheath, 
a network of hornlike material called neurokeratin, holding in its meshes a fat- 
like substance. This sheath consists of segments separated by clear fissures (seg- 
ments of Lantermann). The medullary sheath is interrupted at intervals by a 
constriction called the node of Ranvier. External to the medullary sheath is a 
clear membrane, the neurilemma (sheath of Schwann) which, at the nodes of 
Ranvier is thickened and contracted down to the axial cord (contraction ring). 
Nerve fibers in the brain and spinal cord have the medullary sheath but no 
neurilemma; fibers of the sympathetic system, except in rare cases, have no 
medullary sheath. Before terminating, all nerve fibers loose the sheaths here 
described. 

2. Nonmedullated, in which there is no medullary sheath, but evidence of a 
thin neurilemma; these are called Remak's fibers. 

Nerve trunks. 

In the peripheral system nerve fibers are grouped to form nerve trunks; 
gathered in bundles called funiculi, the fibers being separated by a fibroelastic 
tissue (endoneurium) continuous with a lamellated sheath surrounding each funi- 
culus (perineurium). Between the lamellae are lymph spaces continuous with 
)>mph clefts between the fibers of the funiculi. The funiculi of a nerve trunk are 
bound together by a sheath of loose fibro-elastic tissue continuous with the peri- 
neurial sheaths, which penetrates between the funiculi, and contains fat-cells, 
blood and lymph vessels, the latter continuous with the lymph spaces of the 
perineurial sheaths. The connective tissue sheath is continued over the fine divis- 
ions of a nerve trunk as the sheath of Henle. 

Termiimtions of peripheral nerves. 

1. Motor nerve-endings. The neuraxis of a motor nerve after breaking up 
into small fibrils passes under the sarcolemma, ending in a telodendrion (end- 
brush) in a mass of sai ooplasm and muscle nuclei, forming an elevation on 
the muscle fiber (Doyere's elevation) in which the sarcoplasm is called the sole- 
plate, the nuclei sole-nuclei, the whole a motor end-plate. 

The medullary sheath stops abruptly at the sarcolemma, with which the 
neurilemma becomes continuous, the sheath of Henle being continued over the 
motor nerve-endings, and containing flattened nuclei (telolemma nuclei). Each 
muscle fiber has an individual motor end-plate. 

In plain muscle fibers and heart muscle the ending is much simpler. The 
cell bodies of the neurones" are situated in the sympathetic ganglia; the non- 
medullated fibers branch to form plexuses around the bundles of muscle fibers; 
from these plexuses naked varicose neuraxes penterate between the muscle cells, 
also forming plexuses. Fine fibers from these plexuses give off lateral twigs which 
terminate on the muscle fiber in one or two small granules. 

2. Sensory nerve endings. 

A. Free sensory nerve-endings. 

The essentials of these are the telodendria of dendrites of peripheral sensory 



physioijOgy, comparative anatomy 55 



neurones, the dendrites of which form the sensory nerves of the peripheral nerve 
trunks. These endings are found in all epithelial tissue, and in fibrous connective 
tissue of certain regions. The fibers branch at the nodes of Ranvier, retaining 
the medullary sheath up to the under surface of the epithelium, then terminate 
as nonmedullated fibers, ending between the cells in small nodules or discs; the 
same general arrangement exists in the connective tissue. 

B. Elicapsulated sensory nerve-endings, constituting two groups. a. With 
thin fibrous tissue capsule, including three types. End bulbs of Krause. Meis- 
sener's corpuscles. Genital corpuscles, b. With lamellated capsule, including the 
following types: Vater-Pacinian corpuscles. Neuro-muscular nerve-endings. Cor- 
puscles of Herbst. Neuro-tendinous nerve-endings. 

Ganglia. 

Are groups of nerve cells, the neurones being in intimate relation with 
neurones of the central nervous system. 

1. Spinal ganglia are situated on the superior roots of the spinal nerves, 
and contain the cell bodies of the sensory neurones; the following cranial ganglia 
are classed with the spinal: Gasserian, Geniculate, Auditory, Jugular, and pet- 
rosal of the 9th nerve. Root and trunk ganglia of the 10th nerve. 

They have a capsule of connective tissue, continuous with the perineurial 
sheaths of incoming and outgoing nerve roots, which sends trabeculae inward 
supporting the nerve tissue. The cell bodies are arranged in layers under the 
capsule, and in rows and clusters between the fib«rs in the ganglia. 

From the periphery small nerve fibers enter the ganglia, terminating by 
forming end plexuses around the cell bodies. 

2. Sympathetic ganglia include those of the two cords, and also the following 
cranial ganglia: Spheno-palatine; otic; ciliary; sublingual, and submaxillary. The 
cardiac, semilunar and hypogastric, and many very small ganglia in the viscera. 
In structure they are like the spinal ganglia; the neurones vary in size, shape 
and number of branches. The neuraxes terminate in plain or heart muscle, or 
glandular tissue, and to a lesser extent in other ganglia, both spinal and sympa- 
thetic. 

White and grey rami coininunicantes. 

From the anterior roots of the spinal nerves, from the first dorsal to the 
fourth lumbar, small medullated nerve fibers pass to the sympathetic ganglia by 
the white rami communicantes. After a course of variable length in which they 
may pass through one or several ganglia they terminate in some ganglion of the 
sympathetic system by forming intracapsular plexuses around the cell bodies of 
neurones. 

Other large medullated nerve fibers pass by the white rami to the sympa- 
thetic ganglia, but pass on through them without forming any connection with 
the neurones contained in them, to end in the viscera by free or special sensory 
nerve -endings. 

The vaso-constrictor nerves pass from the cord by the white rami as medul- 
lated fibers, to the sympathetic ganglia where they loose the medullary sheath, 
continuing as nonmedullated fibers to the blood vessels of all parts of the body 
except the cord and limbs. The vaso-constrictor nerves to these parts are 
given off from the same nerves in the ganglia, return to the cord as gray rami, 
supplying the vessels of the cord, and passing to the vessels of the limbs by 
the brachial and sacral plexuses. 

Neuroglia : 

Is a supporting tissue found in the central nervous system, consisting of 
triangular or quadrangular cells with processes of protoplasm extending from the 



56 VETERINARY ANATOMY, HISTOLOGY, 

angles, and fibrils which pass through the cell or are buried in tlae protoplasm. 

The gray matter of the brain and cord is composed of cell bodies and 
dendrites; the white matter and nerve trunks of nerve fibers. 

III. PHYSIOLOGY OF THE NERVOUS SYSTEM. 

Nerves: — Nerves are classed physiologically as afferent and efferent. 

1. Afferent: — Carrying impulses to the brain or nerve centers in the brain 
or cord. 

a. Of special sense; sight, hearing, taste, smell, etc. 

b. Of sensation; pain, heat, cold, etc. 

c. Impulses leading to reflex acts of which the mind is unconscious. 

2. Efferent; conveying impulses from the centers to the periphery; mostly 
motor Impulses causing contraction of voluntary muscles, or regulating the 
tension of involuntary muscles of blood vessels, hollow viscera, ducts of glands, 
etc. Or may be inhibitory, slowing heart action, peristalsis, respiratory move- 
ments; dilating bloodvessels. Or secretory, increasing or decreasing action of 
glaiids. Each kind of impluse may not have a special set of nerves; a sensation 
of heat, cold or pain may pass over the same nerves, yet the nerves that convey 
the sensation of smell from the nose do not convey painful sensation from 
the same area. 

There are distinct channels for afferent and efferent impulses. 

Excitability of Nerves: 

Chemical, mechanical, or electrical stimuli applied to a nerve will promote 
the same kind of impulse as the natural stimulus; in a sensory nerve pain; 
a motor nerve muscular contraction, etc. 

Spinal Nerves: 

Are all mixed nerves external to the point at which the roots unite; the 
superior root contains afferent fibers only; conveying impressions to the centers. 
The inferior root efferent fibers conveying motor, vaso-motor, secretory, inhibi- 
tory or other impulses from the centers to the periphery. Vaso-constrictor 
impulses travel from the cord by the white rami in the inferior roots to the 
lateral sympathetic ganglia, and continue to the head, neck, and viscera. Fibers 
convejdng vaso-constrictor impulses to the cord and extremities leave the white 
ranu in the lateral sympathetic ganglia, return to the cord as gray rami, and 
pass to the limbs by the brachial and sacral plexuses. Vaso-dilator nerves 
are described in the chapter on the blood. 

The inferior roots supply motor impulses to all voluntary muscles except 
those of the face; contracting and dilating impulses to all hollow viscera, blood 
vessels, ducts of glands, etc. Secretory impulses to glands, and trophic impulses 
to the tissues. 

The superior roots supply sensory nerves to the entire body except to 
certain parts of the face. 

l'\inotions of the Cord: 

It is the path by which impulses travel to and from the brain; contains 
centers controlling many vital functions, as the ano-spinal; vesico-st)inal; 
vaso-motor; sweat and trophic centers. 

Reflex Action: 

The structures necessary for a reflex act are: 

1. An afferent nerve to carry the impression to a nerve center. 

2. A center in which outgoing impulses are generated. 

3. An efferent nerve to convey impulses to the periphery. 



PHYSIOLOGY, COMPAKATIVE ANATOMY 57 

The cord may be regarded as a series of centers lying end to end; eacli 
capable of a certain amount of independent action, afferent impulses reaching 
them by the superior roots, and efferent impulses leaving them over the inferior 
roots. Some of these centers are wholly or partially under control of the will; 
as the ano-spinal governing the act of defecation; the vesico-spinal governmg 
the act of micturition. Others are wholly involuntary, as the vaso-motor and 
secretory centers. 

The cord also assists in co-ordinating muscular movements, as in the con- 
traction of related gioups of muscles, their action being so harmonized that 
perfect motion is accomplished. 

Course of Iniimlses in the cord: 

1. Sensory impulses are conveyed to the brain by both the white and gray 
matter of the posterior columns, crossing, as a rule, to the opposite side soon 
after entering the cord, a small number of fibers crossing in the medulla or 
cerebellum, but all terminating in the cerebrum on the side opposite to that on 
which they enter. 

2. Motor impulses; all voluntary motor impulses originate in the cortex of 
the cerebrum, travel dirc.ct to the bulb (medulla) where they cross over and 
run down the opposite side of the cord in the anterior columns. The motor 
nerves not only convey impulses which are the result of stimuli received over 
afferent fibers, or originating in the cerebrum, but also maintain a constant tonic 
action in all muscle fibers, both voluntary and involuntary. Injury of a motor 
nerve to a voluntary muscle renders contraction impossible and at the same time 
causes a relaxation of the muscle, so that the part drops. Section of vaso-motor 
nerves causes a dilatation of the vessels supplied by it, showing that the muscle 
fibers were contracted to a degree. 

Functions of the Medulla Oblongata: 

It is the pathway between the cord and brain; the crossing point of motor 
fibers, and of such sensory fibers as do not cross in the cord. Centers governing 
the vital organs are located here; respiration, heart action, circulation, secre- 
tion of saliva, swallowing, vomiting and control of the digestive tract from 
■ the mouth to the stomach. All cranial nerves except those of sight, smell and 
motor nerves to the eyeball have their origen in the medulla. 

Functions of the Pons Varolii: 

Connects the cerebrum with the medulla and cerebellum; conducts afferent 
and efferent impulses up and down . 

Functions of the Cerebellum: 

The cerebellum acts on the muscles of the same side of the body, in con- 
junction with the cerebral hemisphere of the opposite side. Fibers leaving the 
cells of the cerebellum pass through its penduncles to the opposite cerebral hemi- 
sphere; impulses passing by these fibers influence the impulses from the cortex 
•of the cerebrum to the periphery; the nature of the impulses sent out by the 
cerebellar cells depending on impressions received by it from the periphery. 
These are of four kinds. 

1. Tactile impressions. The importance of impulses from the skin is shown in 
diseases of the sensory tracts; loss of sensation in the soles of the feet has the 
same effect, the patient being unable to maintain his balance with his eyes closed. 

2. Muscular impressions. Sensory nerves carry impressions from the muscles 
to the cord by the superior roots; the impulses ascend to the cerebellum, and 
by these impulses we know what our muscles are doing; the impression passing 
from the cerebellar cells to the cerebrum. Loss of this muscular sense renders 
co-ordination impossible. 



58 VETERINARY ANATOIVIY, HISTOIX)GY, 

3. Visual impressions. Tlie loss of vision in animals frequently causes ir- 
regular movements; and all movements are halting and uncertain. A blind horse 
can be detected by the way he walks. 

4. Labyrinthine impressions. From the ampulla of the utricle and saccule, 
and from the cristae of the ampullae of the semicircular canals, hairlike process 
similar to those in the organ of Corti, project into the endolymph filling these 
cavities. The variation in pressure of the endolymph on one or the other of these 
groups of hairlike processes, caused by movement of the head, generates impulses 
which travel by branches of the eighth nerves to the cerebellum; there they 
are transferred by the cerebellar cells to the opposite cerebral hemisphere, and 
the animal is enabled to co-ordinate muscular movements, and maintain his 
balance, loss of these impressions causes a staggering gait. 

Functions of the cerebrum : 

From the anterior part of the gray matter consciousness and intelligence 
proceed. From the lateral portions motor impulses are sent to the periphery. 
While sensory impressions are received by the posterior region. 

Functions of the Cranial Nerves: 

1. Olfactory; the nerve of the special sense of smell. 

2. Optic; nerve of the special sense of sight. 

3. Motor oculi; motor to all the muscles of the eyeball except the superior 
oblique, external rectus, and external half of the retractor. Motor from the 
ciliary ganglion to the ciliary muscle and constrictor of the pupil. 

4. Pathetic; motor to the superior oblique. 

5. Tri-facial; a mixed nerve having three divisions. 

a. Ophthalmic; sensory to brow, palate, nostrils, lachrymal gland, and mem- 
brana nictitans; sympathetic motor fibers from the ciliary ganglion to the 
radiating muscle of the iris. 

b. Superior maxillary; sensory to the orbit palate, nostrils, teeth and upper 
lip. 

c. Inferior maxillary; a mixed nerve. Sensory to the lower teeth, lips and 
anterior two-thirds of the tongue; special sense of taste, and motor to the 
muscles of mastication and mylo-hyoid. Filaments to the parotid, molar, and 
buccal glands. 

6. Abducens; motor to the external rectus. 

7. Facial; motor to the muscles of the middle ear, external ear, lips, cheeks, 
nostrils, and orbit. Sensory fibers from the vagus to the tongue, by the chorda 
tympani through the fifth nerve; and taste fibers from the glosso-pharyngeal. 

8. Auditory; nerve of the special sense of hearing, and the sense of equili- 
brium. The cochlear branch to the organ of Corti conveys impulses of sound to 
the cerebrum. A branch of the cochlear division to the macula of the saccule 
and the crista of the posterior canal; and the vestibular branch of the eighth 
to the macula of the utricle and cristae of the superior and horizontal canals 
convey impressions of equilibuum to the cerebellum. 

9. Glosso-pharyngeal; a mixed nerve. Motor to the pharynx; sensory to the 
posterior third of the tongue, soft palate, pharynx, and epiglottis; special sense 
of taste to the taste buds of the tongue. 

10. Vagus (pneumogastric) ; a mixed nerve. Motor to the pharynx crico- 
pharyngeus muscle, oesophagus, all intrinsic muscles of the larynx except the 
crico-thyroid. Motor to the stomach (accelerator). Secretory nerves to the 
gastric glands, pancreas, glycogenic cells of the liver. Motor to the trachea, 
bronchi and lungs. Sensory to the mucous membrane of the larynx, trachea, 



PHYSIOLiOGY, COMPARATIVE ANATOMY 59 

bronchi and lungs; oesophagus and stomach. Inhibitory to the heart and 
respiratory center; accelerator and depressor to the heart. 

11. Spinal accessory; motor to the sterno-maxiliari3, trapezius and levator 
humeri muscles; and motor and cardio-inhibitory fibers to the vagus. 

12. Hypo-glassal; motor to he tongue and depressor muscles of the larynx. 

Functions of the SjTn pathetic System: 

These nerves supply the blood vessels, viscera and glands, and will be 
considered in the chapters on these organs. 



CHAPTER VII. 
ANATOMY OF THE DIGESTIVE SYSTEM. 

The digestive system of the horse consists of a musculo-membraneous 
tube extending from the mouth to the anus, called the alimentary canal, having 
dilated portions, secreting glands in the walls, and accessory organs, and glands 
external to the canal which pour their secretions into the canal by ducts. The 
divisions of the canal are: 

The mouth, pharynx, oesophagus, stomacli, small intestines (duodemmi 
jejunum. Ileum) and lai'ge intestines (caecum, great colon, floating color, rec- 
tum) the posterior opening being the anus. 

Mouth: — Boundaries; anterior, lips; posterior, soft palate; superior, hard 
palate; inferior, tongue; lateral, cheeks. Lining the mouth is a mucous mem- 
brane covered by stratified epithelium; having numerous glands secreting mucus. 

Teeth, are twenty-four molar, twelve incisor, and four canine (often absent In 
the female). 

Salivary glands are, the parotid opening in the cheek by Steno's duct; sub- 
maxillary, opening in front of the fraenum linguae by Whartons duct; sublingual, 
opening in the sublingual crest by the ducts of Rivinus; minor salivary glands 
are, molar, labial, lingual, and staphyline (Strangeway). 

The sofe palate in the horse forms a complete wall between the mouth 
and the pharynx. 

The pharynx, is a cavity common to the digestive and respiratory systems; 
it is bounded anteriorly by the soft pxlate, opening into it, the mouth, osophagus, 
larynx, nasal chambers and Eustacian tubes. The walls of the pharynx consist of 
an external muscular layer, (seven pairs), internal layer, of mucous membrane. 

The oesophagvis extends from the pharynx to the stomach; consisting of an 
external muscular coat, and an internal mucous membrane; the muscular coat 
of an external longitudinal layer, and an inner circular, layer; between this and 
the mucous layer is one of loose areolar tissue. 

The stomach; lies in the left hypochondriac and epigastric regions; it con- 
sists of four coats; external serous; next to this a muscular coat of three layers, 
external longitudinal, middle circular, internal oblique; the internal coat is 
mucous membrane, between this and the muscular coat is a layer of areolar 
tissue. The inner coat consists of two distinct structures; the left half is a thick 
layer of stratified epithelium, white and skin like, called the cuticular portion; 
the right half is a layer of columnar epithelium, soft, velvety, pink color, and 
is the true digestive stomach. 



60 VETERIIVAIiY ANATOMY, HISTOLOGY, 

Glands of the stomach are: in the cuticular portion mucous glands only; 
in the right portion, glands secreing pepsin, hydrochloric acid, rennin and also 
mucous glands. 

Small Ditestines: — E-'xtend from the lower opening of the stomach (pylorus) 
to the caecum (ileo-caecal junction). It consists of four coats; external, serous; 
muscular, two layers, external longitudinal, internal circular; internal mucous 
membrane covered by colmunar epitelium, and between this and the muscular a 
layer of areolar tissue. 

Glands of the small Intestuie: Brunners found in the duodenum only; 
Liieberkuhns; in all parts of the sniail and large intestines; lymphoid nodules, 
singly (solitai-y follicles) and in groups (Peyer's patches) in the areolar tissue. 
are not true secreting glands, and have no openings into the intestines. 

Caecum: — Is a large pointed sack, thirty-six inches in length, capacity, six 
gallons, consists of three coats; external serous, middle muscular, the longitud- 
inal layer consisting of several muscular bands only, the inner layer circular; 
the inner coat is mucous membrane. 

Great colon is nine to eleven feet in length, capacity eighteen gallons; three 
coats; external serous; middle muscular consisting of irregular longitudinal bands 
and an inner circular layer; it is described in four portions (first, second, third, 
and fourth.) 

Floating Colon: — Length, ten feet; three coats; serous, muscular consists of 
two longitudinal bands and an inner circular layer; inner coat mucous membrane. 

Rectum: — Extends from the colon to the anus, and resembles the colon 
in structure. 

Anus: — Is the posterior opening of the alimentary canal; and is kept closed 
by the sphincter ani, a circular layer of muscle fibers. 

Tlie abdominal cavity is that part of the body lying between the thorax and 
the pelvis. Bounded in front by the diaphragm, above by the lumbar region, 
laterally and below by the abdominal muscles, and posteriorly by the pelvis. It 
is lined by a serous membrane, the peritoneum, which also covers the viscera 
contained in it, and by folds and bands supports the various organs in place; 
and are called messenteries when they attach organs to the abdominal walls; 
the messentary proper supports the small intestines; the meso-colon, the great 
colon, the meso-caecum, the caecum, the colic messentary, the floating colon, 
and the meso-rectum, the rectum. 

These folds are called omenta, when binding one organ to another; they are; 
the gastro-colic from the stomach and duodenum to the colon; the gastro-hepatic 
from the stomach to the liver; the gastro-splenic from the stomach to the 
spleen. 

Ligaments are folds of peritoneum strengthened by fibrous tissue, and will 
be described with the organs to which they attach. 

Tlie blood vessels have been described in the anatony of the circulation. 

Tlie nerves are the right and left pneumogastric, and sympathetic. 

The glands external to the canal which assist in digestion are the liver, and 
pancreas in the abdominal cavity, and the salivary glands. 

Salivary Glands are: — 1. The parotid; long and flat, its upper extremity 
surrounds the base of the ear; its inner surface lies on the guttural pouch, its 
posterior border on the wing of the atlas, its anterior on the border of the lower 
jaw, and its lower extremity in the angle of the jugular and glosso-facial veins; 
it is covered externally by the skin and deprimens aurem muscle. It consists of 
lobules of secreting cells, and ducts which unite to form one large duct which 
passes to the mouth over the cheek with the facial artery, entering the mouth 



PHYSIOLOGY, COIVIPAKATIVE ANATOMY 61 

opposite the third upper molar tooth. 2. The submaxillary; long, thin, crescentic; 
extends from the wing of the atlas to the body of the hyoid, in the maxillary 
space, enters the mouth as described (see mouth). 3. Sunlingual, small and 
thin, extends along the border of the tongue, from the spur process of the 
hyoid to the maxillary symphisis, its upper border in contact with the mucous 
membrane of the mouth, which it enters under the tongue by the ducts of 
Rivinus. 

The liver is the largest gland in the body, lies in the abdominal cavity, to 
the front and right of the stomach, its anterior surface on the diaphragm. Its 
ligaments are six; the suspensory, froi.i the anterior surface to the diaphragm 
and abdominal floor; coronary from the anterior fissure to the diaphragm; right 
and left lateral from so named lobes to the diaphragm; Spigelian from this lobe 
to the right kidney, and the round from the umbilicus to the anterior fissure. It 
has two surfaces and a circumference; on the anterior surface a vertical fissure 
for the posterior vena cava; on the posterior a transverse fissure, by which 
arteries, nerves, and portal vein enter, and bile ducts leave. On the lower 
border two fissures divide it into three lobes, right, middle and left; on the 
upper posterior surface the Spigelian and caudate lobes, and on the lower, the 
quadrate lobe. It is covered externally by the serous coat, under which is a 
fibrous coat continuous with the areolar tissue separating the lobules. It 
consists of lobules of secreting cells, and ducts which unite to form the 
hepatic duct, entering the duodenum. 

The blood vessels consists of two systems; the hepatic artery supplying 
nutritive, and the portal vein functional, blood; capillaries from both are united 
to form the hepatic veins which enter the posterior vena cava. 

Nerves are from the coeliac plexus of the sympathetic. . 

The pancreas, lies behind the stomach, below the posterior aorta and vena 
cava, above the base of the caecum; it resembles the salivary glands in structure; 
its ducts uniting to form one, the duct of Wirsung, which enters the duodenum 
with the hepatic duct, sometimes as one. 

n. HISTOLOGY OF DIGESTIVE SYSTEM. 

Tlie Mouth: 

Is lined by stratified squamous epithelium resting on a submucosa of con- 
nective tissue with elastic fibrils. Numerous mucous and several small salivary 
glands lie in or beneath the mucous membrane, opening on its surface. Sensorj' 
nerves terminate in Krause's end bulbs and free sensory nerve-endings. 

Teeth: — Consist of the crown, or part above the gum; table, the part in wear; 
neck, the part clasped by the gum; root, the part set in the alveolus. Three 
substances make up the tooth. 

1. Enamel, covering the crown, except that in the teeth of herbivora the 
table consists of dentin with one or two rings of enamel set in its surface. 
Enamel consists of columns set with the ends toward the surface of the tooth, 
and united by cement substance. 

2. Dentin; forms the bulk of the tooth, is a fibrillar substance and mineral 
matter. Consists of tubles, (dentinal tubules) originating in the pulp cavity, 
anastomosing by side branches. Each tubule contains a fibril (dentinal fibril) 
which is a filiform prolongation of a pulp cell (odontoblast.) 

3. Cementum; consists of bone tissue, the lamellae of which contain no 
Haversion canals, but many fibers of Sharpey, usually uncalcified. In the 
root is a cavity opening at the point of the root by the apical foramen; in this 



62 VETERINARY ANATOMY, HISTOLOGY, 

cavity is the tooth pulp, consisting of connective tissue fibrils and branched cella 
with a semifluid ground substance. The surface of the pulp is covered by a 
layer of cells (odontoblasts) from which fibrils extend into the dentinal canals. 
The tooth is joined to the alveolus by the peridental membrane continuous with 
Sharpey's fibers in the cementum and alveolus. 

DeveIoi)nient : 

In the enamel groove along the inner edge of the fetal jaw a ridge (enamel 
ledge) rises; a bulb (enamel germ) develops at the point at which each tooth 
grows; into this the dental papillae push, grow upward and are soon covered by 
the caplike enamel organs, the cells of which develop into the enamel prisms. 
At the periphery of the dentinal papillae there is a differentiated layer of 
columnar cells called odontoblasts which form the dentin. At this time a con- 
nective tissue mantel, the dental sac, forms around each enamel germ, from 
which the cementum is later developed. The milk teeth are in due time absorbed 
by cells called odontoclasts, the crown being thrown off by the permanent 
tooth as it rises above the gum. 

Tongue: — Covered by stratified epithelium, having papillae of three kinds; 
filiform, fungiform and circumvallate. Taste buds are the essential organs of 
the sense of taste; are ovoid, imbedded in the epithelium ba^e downward, 
opening on the surface by a minute opening, the taste pore. Numerous lymph 
nodes and follicles are imbedded in the mucous membrane. 

Salivary Glands: 

Are compound tubulo-alveolar glands; the ducts branch to form small inter- 
lobular dtfcts which run in the connective tissue between the lobules; these grive 
off sublobular ducts, and these, lobar ducts which divide to form two or three 
intralobular ducts. 

The latter radiate toward the periphery of the lobule, terminating in inter- 
mediate ducts which communicate with the secretory tubules. The cells of the 
secreting tubules of the parotid are cubical, nucleated, filled with zymogen 
granules which disappear as secretion advances. In the sublingual there are 
no intermediate ducts; in the tubules are two varieties of cells, one secreting 
mucus, the other a serous fluid. These cells are found in crescentic groups, 
called the crescents of Gianuzzi, or demilunes of Heidenhain. According to recent 
observations (by Solger) this is a mixed gland. The submaxillary is also a mixed 
gland; having tubules secreting mucin, and others secreting a serous fluid. 

Arteries: — Run with the ducts, forming capillary net works around the 
tubules. 

Nerves: — From small sympathetic ganglia, the sublingual and submaxillary, 
follow the ducts to form plexuses outside the basement mem-brane of the acini 
(epilamellar plexus) from which branches penetrate the membrane to from second 
plexuses (hypolamellar) or end on the cells in small granules. Sensory nerve 
endings also follow the ducts, terminating in free sensory nerve-endings in the 
epithelium. Nerve fibers of the chorda tympani terminate in end-baskets inclos- 
ing cell bodies of the neurones in the sympathetic gangelia. 

Pharynx: — Resembles the mouth, the epithelium resting on a well developed 
layer of fibro-elastic tissue. 

Oesophagus : 

Is lined by stratified pavement epithelium resting on fibro-elastic tissue; 
beneath this a muscularis mucosae, which rests on another loose layer of fibro- 
elastic tissue. External to this is the circular and longitudinal layers of muscle 
fibers, striated in the upper third, unstriated in the lower two-thirds, but all 
involuntary. The glands secrete mucin. 



PHYSIOLOGY, COMPARATIVE ANATOMY 63 

Stomach: — The left half is lined by stratified pavement epithelium, white 
and rough, called the cuticular membrane, having- mucous glands only. The right 
half is lined by a single layer of columnar epithelium, resting on a mucosa of 
adenoid tissue consisting of fine elastic fibers which fill the spaces between the 
glands, forming a thin layer under them, and resting on a muscularis musocae; 
these structures together forming the mucous membrane. This rests on a sub- 
mucosa of loose connective tissue, external to this is the coat of plain muscle 
fibers, covered by peritoneum. 

Glands of the Stomach: 

In the left half, mucous glands only. In the right half are glands containing 
two kinds of cells; parietal cells, lying against the gland wall, secreting 
hydrochloric acid; and chief cells occupying the lumen of the gland, or lying on 
a basement membrane, secreting pepsin and rennin. As they approach the 
pylorus the parietal cells dissappear, and pepsin and rennin only are secreted. 
All gastric glands have cells which secrete mucin. 

Intestines, Small and Large: 

Resemble in structure the right half of the stomach. In the small the 
submucosa rises in leaflike projections into the lumen of the tube forming 
transverse processes called valvulae conniventes, which are covered by mucous 
membrane. 

Glands of the Intestines: 

In the duodenum, branched tubulo-alveolar glands (of Brunner) the bodies 
buried in the submucosa, the ducts opening between the villi or into the glands 
of Lleberkuhn. Throughout the small and large intestine are simple tubular 
glands, the crypts of Lieberkuhn. Lymph nodes, singy (solitary follicles) or in 
groups (Peyer's patches) are found throughout the small intestines and colon. 

VilU: — Are fingerlike processes rising on the mucous membrane of the small 
intestines; each villus contains a^ central tubule the lacteal vessel, which empties 
into lymph vessels which pass by way of the messenteric vessels to the thoracic 
duct. Surrounding the tubule is a laj^er of plain muscle fibers; between the 
muscle fibers and a basement membrane a small artery enters the base of thfi 
villus, passes to the apex where it breaks up into capillaries, the vein leaving 
in the same way. Resting on the basement membrane, covering the villus ex- 
ternally is a layer of columnar epithelium. 

Arteries: — Of the stomach form plexuses in the muscular coat, submucosa 
and beneath the muscularis mucosae, from which capillaries pass to form net 
works around the glands. 

In the intestines like plexuses are formed; from these one series enters the 
villi, loose the muscular coat and form capillaries at the summit. Another series 
form capillary net works round the glands as in the stomach. 

Nerve9:^The alimentary canal receives its nerves from sympathetic neurones 
the cell bodies of which are grouped in two plexuses. One between the layers 
of the muscular coat, the mesenteric or Auerbachs, non-medullated fibers from 
this plexus terminate on the muscle fibers of both layers. The other plexus, 
Meisseners, in the submucosa, communicates with Auerbach's, but the termina- 
tion of its fibers is uncertain. Medullated fibers reaching the digestive canal by 
way of the mesentary end in terminal end-baskets around the cell bodies of 
sympathetic neurones in these ganglia. 

The Liver: 

Is a lobular, tubular gland developed from a diverticulum of the intestine. 
Covered externally by the peritoneum, under which is a fibro-elastic membrane 



64 VETEKEVAKY ANATOMY, HISTOLOGY, 

(Glisson's capsule) which sends processes into the substance of the gland dividing 
it into lobules. 

From the center of each lobule toward its periphery extend strands of 
liver cells called hepatic cords; the cells are polyhedral and between their sur- 
faces are spaces which form bile capillaries; grooves on their angles forming 
channels for the blood capillaries. The cells show a central area of protoplasm 
and an external area of paraplasm which is granular, and contains glycogen, 
and secretion vacuoles, which are due to the confluence of minute drops of 
bile forming a globule, which is discharged into the bile capillary by a small 
connecting tubule. The bile capillaries follow the course of the hepatic cords, 
empty into inter-lobular bile vessels which unite to form the hepatic ducts. 

Blood Vessels of the Ldver: 

1. Functional; consists of the portal system, entering the transverse fissure 
as the portal vein, its branches encircle the lobules as interlobular veins from 
which small branches enter the lobule, break up into capillaries which form 
a net work around the hepatic cords. These capillaries unite in the center of the 
lobule to form the intralobular vein, these uniting form sublobular veins which 
form large branches called hepatic veins leaving the liver at the anterior fissure. 

2. Nutritive blood reaches the liver by the hepatic artery, follows the course 
of the portal blood, its capillaries uniting with it to form the hepatic veins. 

The bile ducts follow the course of the portal veins leaving the liver 
at the transverse fissure. 

liymphatics: 

Begin as perivascular spaces in the lobule, communicate with perilobular 
lymph spaces, the vessels following the course of the bile vessels. 

Nerves of the Liver: 

Are from the vagi and sympathetic; accompany the portal vessels on which 
they form plexuses, and to which they give branches, their telodendria ending in 
knoblike terminals on the hepatic cells. The vasomotor nerves accompany th'» 
artery, terminating in the typical manner. 

The Pancreas: 

Is a compound branched alveolar gland; the alveoli lined by secreting cells 
having a homogenous base and granular area bordering on the lumen, the 
zymogen granules dissappear as the gland becomes active, to reappear during rest. 

Each alveolus connects with an intermediate tubule which enters an inter- 
lobular duct, these merge to form excretory ducts ending in the duct of Wirsung, 
whi;h enters the duodenum with the hepatic duct. Groups of cells differing 
from the secreting cells in size and structure are found among the tubules, 
separated from them by connective tissue, called areas of Langerhans. 

ni. PHYSIOLOGY OF THE DIGESTIVE SYSTEM. 

In the Mouth: 

Food is taken up by the lips, or when the animal is grazing bitten off by the 
incisor teeth; crushed by the molars, moistened by the saliva and passed under 
the soft palate by the tongue and muscles of the cheeks. By successive con- 
tractions of the muscles of the pharynx and oesophagus the food is carried to 
the stomach, the act being involuntary after the food reaches the pharynx. 

Functions of the Saliva: 

Moistens the food, and by the ferment, ptyalin, the starches are changed to 
sugar. The ptyalin being alkaline continues its action until neutralized by the 
acid gastric juice. 



PHYSIOLOGY, COTVtPAKATIVE ANATOMY Gi 

Functions of the Stomach: 

In the horse the left half of the stomach acts as a preparatory organ to the 
true digestive stomach. In the right side the pepsin aided by the hydrochloric 
acid, without which pepsin in inactive, changes proteids to peptones and dissolves 
the proteid envelope of fat cells. Milk is coagulated by rennin; and the cellulose 
walls of vegetable cells is partially broken up by a ferment pre-existent in the 
cell. 

FeiTnents of the Intestines: 

Fi'oni the Pancreas: 

1. Trypsin, changes proteids to peptones. 

2. Amylopsin, changes starches to maltose. 

3. Steapsin, changes fats to fatty acids' and glycerin. 
From the Liver: 

Bile, alkaline reaction, neutralises the acid chyme, emulsifies and saponifies 
fats. 

From Intestinal Glands; Succiis Enteiiciis: 

1. Lactase, found in animals taking milk, splits milk sugar. 

2. Invertin, changes sugar and maltose to glucose. 

3. Erepsin, breaks up peptones and proteoses into simpler molecules. 

4. Enterokinase, intensifies the action of trypsin and steapsin. 
Digestion in the Intestines: 

The acid reaction of the chyme is changed to alkaline by the bile and 
other secretions; proteids and peptones are broken up into simpler substances; 
starches are changed to sugar, and cane sugar and maltose to glucose; fats are 
emulsified, saponified and changed to fatty acids and glycerine. 

Absorption : 

In the stomach; glucose, peptones and water are absorbed in small amounts. 

In the intestines; peptones and other products of proteid digestion are 
absorbed by the columnar epithelium, pass to the blood capillaries of the portal 
system, pass by way of the liver to the posterior vena cava into the right 
auricle. 

Fats are absorbed as fatty acids and glycerine by the lacteals, pass to the 
thoracic duct, and by way of the anterior vena cava to the right auricle. 

Functions of the LiAcr: 

1. Glycogenic function; changes sugar to glycogen (animal starch) stores 
It in the liver cells, and as required by the body re-converts it to sugar by a 
ferment (liver lactase) present in the cells, returning it to the blood as glucose. 

2. Changes fatty acids and glycerine to lecithin. Acts as a storehouse for 
fats in animals having little adipose tissue. 

3. Excretion of ammonia and excess of proteids by conversion to urea. 

4. Excretion of waste hemoglobin and storing of iron for future use. 

5. Excretion of other poisonous matters in the bile. 

' Assimilation of food and disposition of products of digestion. 

1. Absorbed food may be used at once for construction or reconstruction. 

2. For production of heat. 

3. For production of energy in the form of mechanical work. 
4. May be stored for future use. 

Construction and repair are carried on principally by the proteid foods. 

Heat is produced principally by the fats and carbo-hydrates. Fatty tissue 
is the main storehouse for unused foods; sugar is stored as glycogen in the 
liver. Proteids are stored in very limited amount except as a result of physical 
training, in increased muscular development. 



66 VETERINARY ANATOMY, HISTOLOGY, 

One-third of the energy liberated is used in the production of mechanical 
work; two thirds in the production of heat. 

A certain degree of heat is necessary to the chemical changes taking 
place. 

Excess of heat is thrown off by radiation and evaporation; by this means an 
even temperature is maintained, although heat is produced much more rapidly 
At some times than at others. In the same way an animal can live in a 
temperature many degrees higher than that of the body. 

Defecation : 

As the food is passed along the alimentary canal by the peristaltic action of 
the intestinal walls, the nutritive matter is absorbed, the residue passing to 
the floating colon and rectum. 

As it accumulates, and presses on the mucous membrane, impulses are 
conveyed the ano-spinal center in the lumbar region; the sphincter muscles relax, 
the glottis is closed, by a forced expiration the abdominal organs are pressed 
backward, aiding the peristalsis in emptying the rectum. This act is completed 
by the action of the levatores ani muscles. In the horse defecation may be 
accomplished by peristalsis alone, making the act possible while the animal 
is in motion. If peristalsis is lost by paralysis of the muscles of the intestines 
defecation is impossible: if thaough disease of the cord the inhibitory action 
of the ano-spinal center is lost and peristalsis remains, feces pass from the 
rectum continuously. 



CHAPTER VIII. 
ANATOMY OF THE RESPIRATORY SYSTEM. 

The organs of respiration consist of; the anterior nares; the nasal chambers, 
each having a superior, middle and inferior meatus; posterior nares, pharynx; 
larynx, trachea; bronchi; lungs; pleura; thorac cavity and muscles of respiration. 

The anterior nares are the anterior openings of the nasal chambers; con- 
sisting of two incomplete cartilaginous rings, attaching by their complete sides, 
in the median line, covered by sRin and muscles externally and mucous membrane 
internally. 

Nasal chambers are two cavities extending from the anterior nares to the 
cribriform plates of the ethmoid above, and the posterior nears below. Each 
side is divided into three meati by the turbinated bones. The chambers are 
lined by mucous membrane, continuous with that of the facial sinuses with 
which the chambers communicate. 

The pharynx is the cavity into which the posterior nares open, (see digestive 
system for description). 

The larynx is a musculo-cartilaginous chamber lying between the pharynx 
and trachea; it consists of seven cartilages, attached to each other by ligaments 
and moved by muscles. The cartilages are; the cricoid, thyroid, epiglottis, two 
arytenoid and two cuneiform. For muscles see muscular system. It is lined 
by mucous membrane continuous with that of the pharynx and trachea; gives 
passage to air, and is the organ of voice. 

The trachea is a musculo-membraneous tube, re-enforced by incomplete 



PHYSIOIXDGY, COMPAKATIVK ANATOMY 67 

rings of cartilage; extends from the larynx to the lungs, is lined by mucous 
membrane. 

The bronchi are divisions of the trachea extending into the lungs, resembling 
it in structure. 

The hings are two musculo-membraneous sacs, consisting of bronchioles, air 
sacs, muscle fibers, blood vessels and nerves. They lie in the thoracic cavity, 
separated by the mediastinum, oesophagus, heart and large blood vessels. 

Tlie pleura is a serous membrane which covers the lungs externally (visceral 
layer) and lines the thoracic cavity (parietal layer). 

Tlioracic cavity is that part of the body inclosed by the sternum, ribs 
dorsal vertebrae, and diaphragm. 

The muscles of respiration are all those having power to distend or compress 
the thoracic cavity; those which distend it are inspiratory; those which compress 
it, expiratory muscles. 

Tlie diaphragm is a fibro-muscular web placed obliquely between the 
thoracic and abdominal cavities, extending from below upward and backward. 
It is the principal muscle of inspiration. 

n. HISTOLOGY OF THE RESPIRATORY SYSTEM. 
Nasal Chambers: 

The respiratory region is lined by pseudo-stratified, ciliated epithelium having 
two strata of nuclei and goblet cells; the ciliate movement is toward the posterior 
nares. The accessory cavities are lined by ciliated epithelium, the ciliate move- 
ment being toward the openings. 

Liarynx: Is lined in the same manner as the nasal chambers, except that 
the true vocal cords, free edges of the epiglottis and upper area of the arytenoid 
cartilages are lined by stratified squamous epithelium. The glands are branched 
tubulo-alveolar mucin secreting baving crescents of Gianuzzi. The arteries end 
in fine capillaries below the epithelium, with a net work of lymph vessels below 
the capillaries. 

Trachea: .Is lined by stratified ciliated columnar epithelium containing goblet 
cells, and resting on a well developed basement membrane. The mucosa is 
fibro-elastic; the ends of the semilunar cartilages are connected by bundles 
of plain muscle fibers. The glands are like those of the larynx. 

Bronchi: Have the same structure as the trachea; the rings of cartilage 
giving place to irregular plates until at a diameter of 0.85 mm. or less no 
cartilage is present. No glands are found in bronchi less that 1 mm. in diameter, 
the elastic fibers predominate, and circular fibers of plain muscle form rings 
about the bronchi. 

The bronchioles are continued as respiratory bronchioles, these divide into 
terminal bronchioles or alveolar ducts, dilated at their distal ends and communi- 
cating by several round openings with spherical cavities called atria. Each atrium 
communicates with several irregular cavities called air sacs; the walls of these 
and also of the atria, terminal and respiratory bronchioles have hemispherical 
bulgings called air cells or lung alveoli. 

The epithelium is ciliated down to the respiratory bronchioles, gradually 
changing to squamous at the distal end of the alveoli. The^respiratory epithelium 
consists of two varieties of cells, large nonnucleated cells resting on the blood 
vessels, and small nucleated cells between them. Terminal bronchioles have 
a layer of plain muscle fibers, with annular thickenings at the openings leading 
into the atria; no muscle fibers are found in the walls of the atria, air sacs or 
air cells, the epithelium of these resting on a very delicate basement membrane 



68 VETEKINAHY ANATOMY, HISTOLOGY, 



over which elastic fibers form a net work. A lobule of lung tissue consists of a 
terminal bronchiole, with the atria, air sacs, air cells, blood and lymph vessels 
and nerves. 

Arteries : 

1. Pulmonary arteries follow the bronchi, a branch entering each lobule 
divides to send a branch to each atrium, from which small arterioles run to 
the air sacs where they break up into radicles, which pass into the sulci between 
the air cells over which they form a net work of capillaries. These capillaries 
are very fine and are sunken into the epithelium of air cells, leaving but a very 
thin basement membrane between the capillary and the air cell. Only one 
such net work is found between two contiguous air cells. The veins collecting 
the blood from the lobules lie at their periphery as far removed from the 
artery as possible. 

2. The bronchial arteries supply nutrient blood, follow the same course as 
the pulmonary branches, form a net work of fine capillaries in the mucous 
membrane, and a coaser one in the connective tissue. These ca^iillariea 
anastomose freely with those of the pulmonary system. The blood leaves the 
lungs by the pulmonary veins, two from each lung entering the left auricle. 

A lymphatic plexus lies on each side of the bronchial cartilages, in bronchioles 
without cartilage but one plexus is found. In the terminal bronchioles two 
lymph vessels go to each vein, one to each artery; beyond the terminal bron- 
chioles no lymphatic vessels are found. 

Pleura: — Consists of a layer of fibro-elastic tissue covered by a layer of 
mesothelial cells. The viscera'l layer receives blood from the piilmq/nary 
vessels, forming a. net work of capillaries from which the blood returns to the 
lungs. 

Nerves: — To the nasal chamber, from the trifacial, their telodendria ending 
in nodules or in simple filaments. 

To the larynx and trachea branches of the vagus. Sensory nerves form sub- 
epithelial plexuses in the trachea and larynx, ending in nodules on the epithelial 
cells. Numerous sympathetic ganglia are found in the trachea and larynx, their 
neuraxes ending on the plain muscle cells. The cell bodies of these sympathetic 
neurones are surrounded by en-baskets formed by telodendria of medullated nerve 
fibers terminating in the ganglia. 

Numerous medullated and nonmedullated nerve fibers accompany the bronchi, 
forming plexuses in the external fibrous layer, from which branches pass to 
end in the muscle tissue, others pass through the outer coats to form subepithelial 
plexuses from which fibrils pass to end beneath the epithelium in minute 
elongated or rounded bulbs. 

TTT . PHYSIOLOGY OF THE RESPIRATORY SYSTEM. 
Respiration: 

The respiratory cycle consists of an expansion of the thorax by which air 
is drawn into the lungs, and a contraction of the thorax by which the air Is 
forced out. 

The first part of the cycle is accomplished by the action of the diaphragm 
which increases the antero-posterior diameter, and the intercostal and other 
muscles which increase the lateral and vertical diameters. As the pressure of the 
atmosphere is many times greater than the elastic resistance of the lungs, the 
air rushes in until the lungs fill the cavity. 

The second part of the cycle is accomplished by the recoil of the elastic 



PHYSIOLOGY, COIMPARATIVE ANATOMY 69 

fibers of the lungs, the inspiratory muscles and the abdominal muscles which 
are distended during inspiration. 

Respired Air: 

Tidal air is the quantity which enters and leaves the lungs at each ordinary 
respiration. 

Complemental air is the quantity that can be taken in after an ordinary 
inspiration. 

Reserve air is the quantity that can be forced out after an ordinary 
expiration. 

Residual air is that remaining in the lungs after a forced expiration. 

Vital capacity is the measure of the total quantity of air that can be taken 
in and expelled at one forced respiratory cycle. 

Changes in Air During Respiration: 

Inspired air contains. Expired air contains. 

Oxygen 21 per cent. 17 per cent. 

Nitrogen 79 per cent. 7 9 per cent. 

Carbonic acid 00 per cent. 04 per cent. 

Watery vapor "Variable. Saturated. 

Temperature Variable. Of the body. 

Clianges in the blood during respiration. 

Arterial blood contains. Venous blood contains. 

Oxygen 20 per cent. 8 to 12 per cent. 

Nitrogen 1 to 2 per cent. 1 to 2 per cent. 

Carbonic acid 40 per cent. 46 per cent. 

Exchange of Gases. 1. In the lungs. 2. In the tissues. 

1. A difference in the quantity of gases in two solutions coming in contact 
will set up a current from that containing the greater to that containing the lesser 
quantity, the flow continuing until both have the same amount. This holds good 
for any number of different gases in solution in the same fluid, and the currents 
may run in both directions at the same time. 

By the law governing the movement of gases the interchange takes place in 
the lungs. The pressure of oxygen in the inhaled air being greater than that in 
the venous blood the current of oxygen passes through the walls of the air cells 
and capillaries to the plasma, is at once taken up by the hemoglobin in chemical 
union, and in this way passes to the tissues. 

The current of carbonic acid flows in the opposite direction; coming to the 
lungs in chemical combination with the sodium salts in the plasma, the pressure 
being much greater than that in the inhaled air, it is at once discharged into the 
air cells. 

The air in the cells is not renewed by the respiratory movements; the residual 
air always remaining quiescent as to these movements, but is kept in constant 
motion and renewed by the currents of gas passing into and out of the cells. 

2. By the same law the interchange in the tissues takes place; the pressure 
of oxygen being greater in the arterial blood than in the tissues, and the affinity 
for oxygen being greater in the tissues the current is toward the latter. The car- 
bonic acid current being in the opposite direction, combining with the sodium 
salts in the plasma. 

Nerves. 

The respiratory center, located in the medulla, consists of an inspiratory and 
an expiratory part. While the force and rhythm of the respiratory acts can be 
varied or temporarily suspended by the will, the center is automatic, responding 



70 VETERLNTAKY ANATOMY, HISTOLOGY, 



to impulses from afferent nerves, yet capable of generating respiratory impulses 
when all afferent nerves are severed. 

Afferent nerves from the lungs are branches of the vagi; at the moment the 
lungs are filled by an inspiratory movement an expiratory impulse passes from 
the lungs to the center, the inspiratory muscles relax, and expiration follows. The 
reverse takes place at the end of the expiratory act. 

Afferent Impulses also reach the center from many other parts; the skin, 
viscera, etc. Inspiration is stimulated by impulses from the skin, but inhibited 
by impulses from the splanchnic area, and both acts are inhibited by stimuli from 
the glosso-pharyngeal. 

The center is also influenced by the condition of the blood; any increase of 
carbonic acid in the blood, or reduction of the oxygen at once stimulates the 
center, and respiration becomes more rapid and deeper. 

Efferent nerves are the motor nerves to all muscles that increase or decrease 
the diameters of the thorax. 

The inspiratory muscles are: The diaphragm, intercostals, serratus anticus, 
levatores costarum. 

Expiratory: Abdominals, intercostals, transversalis costarum, serratus pos- 
ticus. 

The inspiratory act is entirely dependent on muscular action; the expiratory 
act is almost entirely a recoil of the inspiratory muscles and elastic tissue of the 
lungs, except in forced expiration, when other muscles are brought into action, 
especially the abdominal muscles. 



CHAPTER IX. 



ANATOMY OF THE URINARY SYSTEAI. 

Urinary organs. 

Kidneys, ureters, bladder, urethra. 

Kidneys. Are placed in the sublumbar region, one on each sjde of the verte- 
bral column, external to and supported by the peritoneum. The upper surface is 
flat and attached to the muscles by areolar tissue; the lower is more convex and 
lies on the peritoneum. The circumference is convex except at the inner border, 
in which there is a notch, the hilus, at which the arteries and nerves enter and 
the veins and ureter leave. 

Longitudinal section shows a cortical portion of a dark red color, and an 
inner medullary portion of lighter color, and at the inner border a cavity, the pel- 
vis, continuous with the ureter. 

Ureter. .Is a tube extending from the hilus of the kidney to the bladder; 
passing along the roof and walls of the abdominal and pelvic cavities to the 
supero-posterior aspect of the bladder, which it enters by piercing the outer 
layer of the muscular coat, passing a short distance between the layers, then 
piercing the inner layer and mucous coat. It consists of three coats; outer fibrous, 
middle muscular, inner mucous. 

Bladder. Is a musculo-membranous organ, placed in the pelvis, below the 
rectum. It consists of three coats; external serous, middle muscular, inner mu- 
cous. It is held in place by ligaments attached to the floor and walls of the pel- 
vis and to the rectum. 



PHYSIOLOGY, COMPARATIVE ANATOMY 71 

Urethra. Is a tube extending from the bladder to the external meatus; in the 
female it terminates in the vulva, and is a simple excretory duct of the bladder. 
In the male it terminates at the glans penis, and is common to the urinary and 
generative systems, and will be fully described with the generative organs. 

The neck of the bladder is surrounded by a thickened layer of muscle fibers, 
the sphincter vesicae, which retains urine in the vessel until relaxed during the 
act of micturition. 

II. HISTOIX)GY OF THE URINARY SYSTEM. 

Kidney. 

Is a branched tubular, lobular gland surrounded by a capsule of fibro-elastic 
tissue, with muscle fibers in its deeper part. In longitudinal median section the 
kidney shows a dark red cortical region, and a lighter medullary portion. It con- 
sists of a number of pyramidal divisions called renal lobes, or Malpighian pyra- 
mids. The secreting portion consists of tubules each presenting the following 
divisions: 

1. Bowman's capsule, a double walled cup surrounding a plexus of capil- 
laries, the glomerulus, the two forming a Malpighian corpuscle, united to the sec- 
ond portion of the tube by a constricted neck. 

2. Proximal convoluted portion, which ends in a tapering section, the end 
segment of Argutinski. 

3. A "U" shaped portion consisting of a descending and ascending limb and 
loop of Henle. 

4. Distal convoluted portion. 

5. Arched collecting portion; the confluence of a number of these forms 
the straight collecting tubules which unite to form the papillary ducts (tubes of 
Bellini) which empty into the pelvis at the apex of the papilla, forming the for- 
amina papillaria in the area cribrosa. 

The Malpighian pyramid consists of medullary substance, its apex projecting 
into the pelvis, from its base a large number of medullary rays extend toward 
the surface of the kidney, called the pyramids of Ferrien, and consists of collecting 
tubules extending into the cortical substance. At the periphery of the kidney the 
cortical substance forms the cortical labyrinth; between the medullary rays it 
forms the cortical processes, and between the Malpighian pyramids it forms the 
columns of Bertini, or septa renis. The capsule forms a double wall around the 
glomerulus; a space between the walls communicates with the lumen of the 
tubule. 

Arteries. 

Enter at the hilus, divide at the septa renis to form arterial arches, which 
pass between the medullary and, cortical portions. From these the intralobular 
arteries arise and penetrate into the cortical processes, where they give off twigs 
which end in the glomeruli. After entering the capsule each twig breaks up into 
several branches, forming separate capillary networks enclosed in fibrous cap- 
sules, dividing the glomerulus into lobules. The efferent vessels are formed by 
the union of branches from each lobule, leave the corpuscle as arteries, form a 
second system of capillaries and gradually become venous. 

Capillaries from the cortical labyrinth and processes unite to form intralobu- 
lar veins; from the Malpighian pyramids they unite to form the "venulae rectae," 
these empty into venous arches corresponding to the arterial arches, the larger 
veins following the course of the arteries to leave the kidney at the pelvis. 

Nei-ves. 

Enter at the hilus, accompany the arteries, ending in the Malpighian cor- 
puscles, epithelium of the tubules and coats of the arteries. 



72 VETERINAIIY ANATOMY, HISTOLOGY, 

Ureter. 

Consists of an outer fibrous coat, a middle muscular of a longitudinal layer 
internally, a circular layer externally, with a second longitudinal layer external 
to this in the lower two thirds. The inner mucous layer is lined by stratified 
transitional epithelium, as is also the pelvis of the kidney and the bladder. 

Bladder 

Consists of an external serous coat, a middle muscular, and an inner mucous. 
The muscular coat presents a felted appearance, the layers not clearly defined. 
The epithelium of these organs is very elastic, changing its shape according to 
the amount of fluid contained. 

Nerves. 

Prom the sympathetic system form ganglia outside the muscular coat of the 
bladder, their telodendria ending on the muscle fibers. Sensory nerve fibers pass 
through these ganglia, pierce the muscular coat and terminate in th'i epithelial 
cells of the inner coat. 

m. PHYSIOIXKiY OF THE URINARY SYSTEM!. 

Secretion. 

In "Bowman's capsule the water filters through the glomerular epithelium by 
blood pres&ure, parsing into the space between the walls and downward into the 
tubule. By increasing the pressure in the arteries with a free flow from tne 
veins the secretion is increased; by increasing the pressure in the glomerulus by 
ligature of the efferent vessels secretion is decreased. 

In the tubules the cells have a selective action, excreting organic and inor- 
ganic solids. The extent of the special action ascribed to different regions of 
the tubule is uncertain. 

ConiiKJsition. 

Color varies within wide limits, ranging from dark amber to almost colorless. 

Specific gravity, horse 1036; ox, 1025; pig, 1020; dog, 1016 to 1060. (Smith) 
This also varies greatly, depending on food, drink and conditions of living, work, 
etc. Turbidity; when warm, is clear; on cooling a precipitate of carbonate of lime 
falls; in the urine of carnivora a cloud of mucin forms. Urea, 80 per cent of the 
waste nitrogen is removed in the urine of herbivora, 90 per cent in that of car- 
nivora, in the form of urea. The remaining 10 per cent to 20 per cent as am- 
monia salts, uric acid, hippuric acid, creatinin, and other bodies in small amounts. 
Sulphur, 90 per cent is excreted as pre-formed sulphates, 10 per cent as etherial 
sulphates. Phosphates; in herbivora are excreted by the intestines; in carnivora 
by the kidneys as phosphates of soda, lime and magnesia. Chlorine; from that in- 
gested, is small in amount in the horse. Pigments; urochrom"e, urobilin, uroery- 
thrin, and hemato-porphyrin. Nucleo-proteid; a mucin like substance. Carbonic 
acid combined with potassium, lime and magnesia. Oxalie acid, combined with 
lime. 

Exci'etion, 

Urine is passed from the kidney to the bladder by the pressure under which 
it is secreted, assisted by rhythmic action of the muscular coats of the ureters. 

"When urine enters the bladder its return into the ureters is prevented by the 
pressure of the contained fluid against the portion of the ureter included between 
the muscular layers of the bladder wall. 

As the vessel fills and the fluid presses on the area of the sphincter vesicae 
an impulse is conveyed to the vesico-spinal center in the cord; the sphincter re- 
laxes; the bladder walls and such muscles as can increase the pressure on the 
bladder exterally, contract, and micturition is accomplished. 



PHYSIOLOGY, COaiPARATIVE ANATOMY 73 

CHAPTER X. 

ANATOMY OF THE GENERATIVE SYSTEM, 

The generative organs of the female are: Ovaries, fallopian tubes, uterus, and 
vagina. 

Ovaries, situated in the sublumbar region, behind the kidneys; attached to 
the broad ligament of the uterus, and by the inner end to the uterus by the liga- 
ment of the ovary. They are covered externally by the peritoneum, beneath which 
is a dense fibrous covering, the tunica albuginea, inclosing a substance consisting 
largely of connective tissue and large cells, the future ovum. 

Tlie fallopian tubes extend from the horns of the uterus, in the free border 
•of the broad ligaments to the ovaries, where the free end terminates in the fim- 
hriae or fringes, arranged in a circle around the opening in the free end, the 
ostium abdominale, one of the processes being attached to the ovary. At the 
inner end the tube is' attached to the horn of the uterus, and opens into it by 
the ostium uterinum. The tube has an external serous coat, a middle muscular 
of two layers, an outer longitudinal and an inner circular. And an inner mucous 
coat in longitudinal folds, and covered by ciliated epithelium which extends to the 
fimbriae. 

Tlie uterus is a musculo-membranous sac situated in the sublumbar and 
pelvic cavities; consisting of a body and two cornua. 

The body is cylindrical, the posterior part, the neck, projects into the vagina, 
the anterior, fundus reaches the intestinal convolutions, the upper surface the 
rectum. The cornua diverge upward and forward from the fundus, continuous 
with the cavity of the uterus and with the fallopian tubes. 

The body is supported by the broad ligaments laterally, the round ligaments 
passing from the upper angles of the body to the internal abdominal rings, the 
recto-uterine to the rectum, and the vesico uterine to the bladder. The uterus 
has an outer serous, middle muscular and inner mucous coat. The openings are, 
the ostium uterinum at the end of each horn, the ostium externum at the outer 
end of the cervix opening into the vagina, and the ostium internum from the 
body into the cervix. 

The A^ag'ina is a membranous canal leading from the uterus to the vulva, 
consisting of muscular fibers and a mucous membrane. 

The vulva is the external orifice of the urino-genital system, is a vertical 
slit, the fissura magna, with two lips and two commisure; the upper commisure 
is narrow, reaching nearly to the rectum, the space between them is the perineum; 
the lower commisure is rounded. In the floor of the vulva in a depression, the 
fossa navicularis is the clitoris, covered by a fold of mucous membrane, the 
prepuce. The external orifice of the urethra (meatus urinarius) opens in the 
floor of the vulva about four inches from tne external opening. 

The generative organs of the male are: The testicles, scrotum, vas deferens, 
vesiculae seminales, urethra, and penis. 

Tlie testicles are two oval glands situated in the scrotum, their long axis 
from before backward. Developed in the abdominal cavity above the peritoneum, 
they pass down through the inguinal canal to the scrotum guided by the guber- 
naculum testes, taking on coverings from the abdominal parieties. 

The scrotum is composed of the skin; the dartos, from the abdominal tunic; 
the spermatic fascia from the external oblique; the cremasteric fascia from the 
internal oblique; the infundibuliform fascia from the transversalis; and two layers 
from the peritoneum, the tunica vaginalis reflexa attached to the fascia, and the 



74 VETERINARY ANATOMY, HISTOLOGY, 

tunica vaginalis propria attached to the testicle. Attached to the upper border 
of the testes is the epididymis, formed by the excretory ducts of the gland, consist- 
ing of a head (globus major) body and tail (globus minor). These ducts unite 
to form the vas deferens, a tube passing from the testes through the inguinal 
canal to the base of the bladder, where it is joined by the duct of the vesiculae 
seminales and enters the urethra, the two ducts forming the ejeculatory duct; it 
has three coats, fibrous, msucular and mucous. 

Tlie vesiculae seminales are two lengthy tubes coiled up to a gland like form, 
on the posterior aspect of the bladder, their ducts unite with the vas deferens to 
form the ejaculatory ducts. 

The penis is the male organ of copulation, containing the urethra in its lower 
border. It consists of an attached and a free partion; the first originates at the 
ischial arch in the pillars or crura which extend to the pelvic brim where the 
free portion begins. It consists of erectile tissue in two structures, the corpus 
cavernosum which forms the upper and lateral parts, and the corpus spongiosum 
which forms the lower central part and contains the urethra, terminating anter- 
iorly in the glans penis, a deep fossa in its apex lodges the meatus urinarius. 

Tlie urethra extends from the neck of .the bladder to the glans penis; divided 
into a prostatic postion passing through the prostate gland; a membraneous por- 
tion between the prostatic portion and the ischial arch; spongy portion from the 
ischial arch to the meatus. This portion is narrow in the middle with a dilata- 
tion, the bulbous portion posteriorly, and the fossa navicularis anteriorly. 

The prostate is a compound racemose gland situated on the postero-superior 
part of the bladder neck; consists of three lobes of reddish grey substance en- 
closed in a fibrous capsule, having several ducts which open in the prostatic sinus. 

Cowpers glands are two small bodies on the sides of the membraneous por- 
tion of the urethra, consist of several lobules held together by connective tissue, 
and open in the urethra by several minute openings. 

II. HISTOIX)GY OF THE GENERATIVE SYSTEM. 
The generative organs of the female are: Ovaries, fallopian tubes, uterus and 
vagina. 

Ovarj'. 

Is covered by peritoneum except at the hilum; here the connective tissue ele- 
ments of the ovarian ligament penetrate into the organ, forming its stroma or 
frame work. The covering of mesothelial cells is differentiated to form the germ- 
inal epithelium; which by a process of invagination into the stroma forms at the 
periphery a zone called the cortex. From the cortex the germinal epithelium 
pushes into the stroma in solid processes forming the prilYiary egg tubes of 
Pfluger; some of the cells of these tubes enlarge to form young ova, others be- 
come the follicular cells surrounding the ova. The primitive eggtubes are divided 
by processes of connective tissue into epithelial nests, separated from the layer 
of germinal epithelium, and imbedded in connective tissue. 

These epithelial nests form several groups, but all are finally changed to form 
typical follicles. 

The typical primitive follicle consists of a large egg-cell (ovum) surrounded 
by a single layer of smaller cells, the follicular cells. Growth takes place by 
mitotic division of the small cells and increase in size of the ovum, which is soon 
surrounded by several layers in which it assumes an eccentric position. In the 
center of the follicle a cavity forms, called the antrum, which increases until it 
nearly surrounds the ovum, which remains attached to the follicular wall, and 
buried in a mass of cells called the discus proligerous; the cells lining the wall 



PHYSIOIiOGY, COMPARATIVE ANATOMY 75 

the stratum granulosum. The vesicle is now called a Graafian follicle, the fluid 
in the antrum is the liquor folliculi, and the layer of cells resting on the ovum the 
corona radiata. 

As the follicle grows the connective tissue forms a membrane around it 
called the thecae folliculi, having an external fibrous, and an inner vascular and 
cellular layer, the tunica externa and interna. 

As the follicle grows the ovum changes; a clear membrane, the zona pellucida 
or vitelline membrane forms inside of the corona radiata, processes from its cells 
passing through pores in the membrane. Between the zona pellucida and the 
protoplasm of the ovum is the perivitelline space; a zone of clear protoplasm next 
to this space contains the germinal vesicle (nucleus) within which is the germinal 
spot (nucleolus). A more central zone of protoplasm contains yolk granules. As 
the. Graafian follicle matures the pedicle of the discus proligerous softens, separ- 
ates, and with the ovum floats free in the antrum; the follicle reaches the surface 
of the ovary, the tunica albuginea and the thecae folliculi become thinned, the 
bloodvessels obliterated, and this region (the stigma) gives way, the ovum being 
discharged. 

Corpus luteuiu. 

After the Graafian follicle ruptures its remaining walls collapse, the cells 
enlarge, develop a yellow pigment (lutein), undergo fatty degeneration and are 
absorbed. The connective tissue atrophies and the corpus albicans remains. 

Fallopian tube. 

Consists of serous, muscular and mucous caots; the mucous membrane has 
four large longitudinal folds, called chief folds, with smaller folds between them; 
all being covered by a layer of ciliated columnar epithelium. The mucosa consists 
of fibro-cellular tissue and a few muscle fibers; the muscular coat of an inner cir- 
cular, and other longitudinal layer; the serous coat of peritoneum. 

Uterus. 

Is lined by ciliated columnar epithelium; the mucosa is fibro-cellular con- 
nective tissue; in both body and cervix are numerous mucous glands. The muscu- 
lar coat consists of an inner and outer longitudinal layer, and a middle circular. 
The serous coat is peritoneum. 

Vagina. 

Is lined by stratified squamous epithelium; the mucosa is fibro-elastic tissue; 
the muscular coat is well developed, and surrounded by a dense layer of connect- 
ive tissue. 

The generative organs of the male are: Testicles, scrotum, vas deferens, vesi- 
culae seminales, urethra and penis. 

Sci*otuni. 

Is the sac in which the testicles lie; its inner wall is lined by the parietal 
layer of the tunica vaginalis, the visceral layer covering the testicle. This is a ser- 
ous membrane derived from the peritoneum. 

Testicle. 

Beneath the serous covering is the tunica albuginea, a dense fibrous cap- 
sule, having on its inner surface a layer of loose areolar tissue and bloodvessels, 
the tunica vasculosa; a thickened portion of the capsule forms the mediastinum 
testis (corpus Highmori) which projects into the substance of the gland. 

From the mediastinum processes radiate toward the periphery dividing the 
gland into lobules, each one occupied by a seminiferous tubule. Beginning at the 
base of the pyramidal lobule, the tubule coils upon itself, passing to the corpus 
Highmori, near which it becomes the straight tubule (tubuli recti). Within the 
corpus these unite to form a network, the rete testis, from which a number of 



76 VETEKIIVARY ANATOMY, HISTOIX)GY, 

convoluted tubules (vasa efferentia) rise, each inclosed in a fibrous sheath (coni 
vasculosi Halleri) constituting the elements of the globus major of the epididymis, 
uniting later to form one canal, the vas epididymidis, also convoluted, forming 
the body and tail (globus minor) of the epididymis. 

Vas aberrans. 

Is a blind canaliculus communicating with the epididymis. 

Vas deferens. 

Is the excretory duct of the testicle, has an internal and external longitudi- 
nal and a middle circular layer of muscle fibers; the mucosa contains many 
elastic fibers, and is lined by stratified ciliated, columnar epithelium. 

Vesiculae seroinales. 

Are two small convoluted tubes, lying coiled up on the supero*posterior part 
of the bladder, consisting of an outer longitudinal and inner circular layer of 
muscle fibers; a thin connective tissue mucosa lined by simple columnar epithel- 
ium. 

Ejaculatory ducts. 

Are formed by the union of the ducts of the vesiculae seminales with the 
vas deferens, emptying into the urethra. 

Cowpers glands. 

Are small bodies situated on the borders of the membranous urethra empty- 
ing into it by long ducts. 

Prostate gland. 

Is a branched tubulo-alveolar gland, resting on the urethra, having an acid 
serous secretion;' the excretoi-y ducts emptying into the urethra. 

Penis. 

Consists of three cylindric masses of erectile tissue, two corpora cavernosa 
lying side by side, the corpus spongiosum containing the urethra below and be- 
tween them, all inclosed in thin skin having no adipose tissue, and no hair fol- 
licles. 

Erectile tissue consists of connective tissue, elastic fibers and plain muscle 
cells, enclosing venous sinuses lined by endothelial cells, and having free com- 
munication with each other. 

Ai'teries of the penis. 

Break up within the septa between the sinuses to form capillaries, some of 
whicTi empty directly into the sinuses; another arterial capillary plexus is formed 
beneath the fibrous tunic of the penis, (tunica albuginea) communicating with a 
deep venous network which empties into the sinuses. There are also anasto- 
moses between the arterial and venous capillaries. This system permits the 
blood to flow through or around the venous sinuses. 

Ui"etln-a. 

Is lined by epithelium varying from stratified transitional in the prostatic 
portion to stratified squamous in the fossa navicularis, resting on a basement 
membrane, which lies on a fibro-elastic mucosa. 

Surface of the urethra. 

Numerous epithelial sacculations in the mucous membrane (glands of Littre) 
are found in the course of the urethra. 

On the floor of the prostatic portion is a narrow longitudinal ridge, the col- 
liculus seminalis (verumontanum), on each side of it a depression, the prostatic 
sinus into which the prostatic ducts open. In the mid line in front of this ridge 
is a depression, the sinus pocularis into Which the ejaculatory ducts open. 

Nerves. 

Of the glans penis terminate in Meissner's corpuscles, end bulbs of Krause, 



PHYSIOLOGY, COMPARATIVE ANATOMY 77 

Pacinian and genital corpuscles. The vaso-dilators are the nervi erigentes coming 
as white rami from the second and third sacral nerves. The internal pudic 
branches from the lumbo-sacral plexus supply the muscles which act as com- 
pressers of the veins of the penis during erection; when these are severed erec- 
tion cannot take place. 

Spermatozoa. 

Are the sexual cells of the male, and are found suspended in the semen, a 
fluid consisting of the secretion of several glands. A spermatosome consists of a 
head, middle piece, and tail or flagellum; the head terminates in a lance like ex- 
tremity; the middle piece is attached to the posterior extremity of the head, 
surrounding the anterior part of the axial thread, a fibrillated process which ex- 
pands anteriorly to form the terminal nodule, a small bulb fitting into a depression 
in the head. The axial thread passes through the center of the tail, terminating 
in a -naked filament, the end piece of Retzius. Between the middle and end piece 
the axial thread is surrounded by a transparent substance, the sheath. A delicate 
process, the accessory thread, runs along the surface of the sheath from the 
middle piece nearly to the end piece. Another process, the marginal thread, 
winds round the axial thread from the middle to the end piece, the space between 
them being filled by the undulating membrane, which expands near the end 
piece to form a wider portion, the rudder membrane. 

III. PHYSIOLOGY OF THE GENERATIVE SYSTEM. 
Copulation. 

Is the act of uniting the sexual organs of the male and female in such a 
manner as to place the sexual cells together, usually within the uterus, or in the 
vagina from which the spermatozoa enter the uterus by fheir own motion. 

The oestroiis cycle. 

The female has cycles of sexual activity consisting of three stages. 

1. The anoestrous stage, during which the sexual organs are at rest. 

2. The prooestrous stage, during which one or more Graafian follicles ma- 
ture, and the fallopian tubes, uterus and vagina are congested. 

3. The oestrous stage, during which coition takes place, the Graafian folicle 
ruptures and discharges the ovum (ovulation), the spermatozoa are discharged 
into the vagina, pass into the uterus, unite with the ovum in the uterus or fallo- 
pian tubes, and impregnation is effected. 

For further changes in the impregnated ovum see works on embryology. 



CHAPTER XI. 



ANATOMY OF THE SKIN AND ITS APPENDAGES. 

The skin. 

Consists of the dermis (cutis vera) which forms the deep layer, is vascular, 
sensitive, and attached to the underlying parts by a layer of areolar tissue which 
contains fat cells (panniculus adiposus). And the epidermis (cuticle) a non-vas- 
cular, insensitive, protective layer of epithelium. 

Glands. 

Sebaceous glands, lodged in the dermis, usually open in a hair follicle, consist 
of a lobulated recess with a short excretory duct. Sudoriferous glands (sweat 



78 VETERINARY ANATOMY, HISTOLOGY, 

glands) lie In the subcutaneous areolar tissue, surrounded By fat, consist of one 
or more small tubes coiled into a ball, the free end opening on the epidermis. 

Hair. 

An appendage of the skin, forms the external covering of most mammals. A 
hair consists of a root, shaft and point.- The root terminates in a bulb, lodged 
in a follicle in the dermis or areolar tissue below it. The shaft and point include 
the portion external to the skin. 

Hoof. 

Developed from the skin, encloses the bones of the foot; consisting of the 
wall, sole and frog. The wall is divided into toe, quarters, heels, bars, external 
and internal surfaces, upper and lower borders. The toe forms the front of the 
hoof; the quarters are between the toe and heels; the heels are the angle formed 
by the wall as it turns inward and forward under the foot, forming the bars 
which meet in the center of the sole to which they are attached. The external 
surface is smooth, covered by a thin layer, the periople. The inner surface con- 
sists of white perpendicular plates, called the keratophyllous tissue (insensitive 
laminae), which fit into depressions in the soft structures, the ridges between 
being the sensitive laminae. The superior border (coronary border) has a 
groove sloping downward and inward, the cutigeral groove, in which the coronary 
band lies. The inferior border is in contact with the ground. The sole fills the 
space between the lower border and bars, is concave below, convex above. The 
frog fills the space between the bars, to which it is attached. The coronary sub- 
stance fills the cutigeral groove, covered by a modification of the skin from 
which the horn of the hoof is secreted; and along its upper border a narrow pro- 
cess, the perioplic ring, which secretes the periople. 

Horns. 

Are developed in the same manner as the hoof, from a membrane covering 
the horn core, and from a pad at the base, consisting of modified skin. 

n. HISTOLOGY OF SIvIN AND APPENDAGES. 

The skin consists of the dermis or corium, derived from the mesoderm; and 
the epidermis or cuticle, derived from the ectoderm. 
Epidermis. 

Consists of two layers; inner Malpighian layer of three strata; external cor- 
nael layer of two strata. 

Inner layer. 

1. A deep stratum of columnar cells resting on the corium. 

2. A middle layer of polygonal cells. 

3. An upper stratum of gradually flattening cells (stratum granulosum). All 
these strata consist of prickle cells, joined by their processes which form inter- 
cellular bridges, between which is a system of channels communicating with 
lymph vessels of the corium. In the stratum granulosum is a substance called 
keratohyalin. 

Outer layer. 

1. Stratum lucidum, consisting of transparent cells, which contain a homo- 
genous substance derived from thie keratohyalin. 

2. An external strata of flattened cells which loose their nuclei, become 
horny and fall off. 

Corium. ' 

1. The pars reticularis, a layer of loose connective tissue fibers, and a retic- 
ulum of elastic fibers. Below this a subcutaneous layer of areolar tissue through 
which strands pass uniting the lower strata of the corium to the superficial fascia; 



PHYSIOLOGY, COMPARATIVE ANATOMY 79 

these strands are the retinaculae cutis, and enclose in their meshes fatty masses 
which form the panniculus adiposus. 

2. The pars papillaris, a dense layer of fine connective tissue fibers and a 
reticulum of elastic fibers; its upper surface covered by papillae over which is a 
very delicate basement membrane on which the basal cells of the epidermis rest. 
The papillae are known as vascular papillae when they contain blood vessels, as 
tactile when they contain nerve fibers. 

Pigment. 

Appears in the stratum papillares of the corium, but principally in the 
basal cells of the epidermis. The source of the pigment is uncertain, but it ap- 
pears to develop from branched connective tissue cells in combination with cer- 
tain bodies called trophoplasts. 

Arteries. 

Anastomose freely in the fascia and subcuticular layer, penetrate the dermis 
to form a network in its lower strata from which branches rise to form a sub- 
papillary plexus; from this plexus branches pass under the rows of papillae, 
supplying- each papilla with a capillary twig. These twigs pass over into venous 
capillaries which form four plexuses, one below another, before uniting to form 
larger vessels. 

Lijiiiphatics. 

Begin in the interspinous spaces in the stratum Malpighii, pass to clefts in 
the corium, which communicates with a sub-papillary plexus, this with a plexus 
in the subcutis. 

Nerves. 

In the tactile papillae the tactile corpuscles of Meissener; in the corium and 
subcutis, end bulbs of Krause, Pacinian corpuscles, Golgi-Mazzoni corpuscles and 
Ruffini's nerve-endings. The bloodvessels receive nerves from the sympathetic. 

Mamniai-y glands. 

Are derived from the basal layers of the epidermis; the gland is divided into 
lobes, these into lobules which are composed of irregular alveoli, lined by a single 
layer of cubical epithelium. At the beginning of secretion fat globules appear in 
the distal ends of the cells, the entire alveolus is enlarged, the end of the cells 
constricted off. then fall into the lumen and pass out as milk. The basal end of 
the cell takes on a new growth and the process is repeated. 

Hair. 

In the third month of fetal life papillary elevations develop on the skin, 
under each papilla the cells of the Malpighian layer proliferate downward to form 
the hair germ; around wliieh the corium forms a connective tissue sheath of two 
layers. The corium now pushes up into the lower end of the hair germ to form 
the hair papilla, the germ being differentiated into an axial portion from which 
the hair and inner root sheath are developed, and a peripheral portion forming 
the outer root sheath and sebaceous glands. The part above the skin is the 
shaft, below the surface the root, the expanded lower end the bulb, the mem- 
branes enclosing it, the root sheaths; the whole termed a hair follicle. 

The hair consists of an external layer of overlying cells, the cuticle; below 
this the cortical layer containing pigment granules; in the axillary portion the 
medullary substance. 

Inner root slieath. 

Consists of three layers; an outer single layer of nonnucleated cells (layer 
of Henle) ; a middle stratum of nucleated cells containing keratohyalin (Huxleya 
layer) ; an inner layer resting on the hair, the inner cuticle. 



80 • VETERINARY ANATOMY, HISTOIXJGY, 

The outer root sheath. 

Consists of an inner layer of prickle cells, and an outer layer of columnar 
cells, both from the Malpighian stratum of the epidermis. The connective tissue 
capsule of the hair follicle consists of an outer layer of loose longitudinal bundles, 
and an inner circular layer of firm fibers, on which rests a basement membrane, 
the glassy layer. 

Shedding of hau-. 

Begins by cornification of the cells of the bulb, which separates it from the 
hair papilla; the cortical portion of the bulb breaks up into a brushlike mass and 
the hair becomes a "club hair." The external root sheath now proliferates down- 
ward, forming a bud from which a new hair with its sheaths and connective 
tissues papilla is developed. The new hair pushes the club hair outward until it 
drops off. 

The arrectores piloiiiin. 

Are small bundles of plain muscle fibers originating from the papillary layer 
of the corium and inserted to the lower part of the connective tissue sheath of 
the follicle. 

Nerves. 

To the follicle reach it below the mouth of the sebaceous gland, forming a 
ring from which fibrils pass upward ending outside the glassy membrane. 

Sweat glands. 

Are simple tubular glands, the secreting portion coiled in the adipose tissue 
or subcutaneous layer, the duct passing through the corium as a straight tube, 
through the epidermis as a spiral opening between the cells. The secreting por- 
tion is lined by a single layer of columnar cells, separated from the basement 
membrane by a longitudinal layer of plain muscle fibers. A capillary network sur- 
rounds the secreting portion. Sympathetic nerves form a network outside the 
basement membrane, called the epilamellar plexus, from which fibrils pierce the 
membrane to end in clusters of small granules on the cells. 

Sebaceous glands. 

Are simple branched alveolar glands developed from the elements of the outer 
root sheath; surrounded by a connective tissue capsule, and lined by a continua- 
tion of the glassy membrane. Inside the glassy membrane two or tnree layers 
of glandular cells from the external root sheath form the secreting elements. The 
central cells gradually change in character, their contents consisting of fat glob- 
ules increase until the entire cell is pushed into the hair follicle, new cells formed 
by proliferation of the basal layer taking their place. 

in. PHYSIOLOGY OF THE SKIN AND ITS APPENDAGES. 

Functions of the skin. 

1. Protective; the sensitive parts beneath are protected from injury from 
violence, heat, moisture, insects and dust. The oily secretion of the sebaceous 
glands renders the skin proof against injury from rain, snow, etc. 

2. Sensory; as an organ of touch the skin is very important to the lower 
animals; the presence of insects, or approach to obstructions being noticed by the 
slightest touch of skin or hair. 

3. Regulates the temperature of the body; the hair protects the body from 
excessive heat or cold externally, and also prevents undue loss of heat from the 
body; if an animal be shaved and the body varnished or inclosed in foil it dies 
from loss of heat by radiation. At the same time an animal can live in a tempera- 
ture many degrees hotter than the body, yet retain a normal temperature, prin- 



PHYSIOLOGY, COMPARATIVE ANATOMY 81 

cipally by dispersion of heat through evaporation of sweat. The excessive heat 
generated in the body by active work is thrown off in the same way. 

4. Excretory; sweat escapes in two forms; as insensible perspiration it is 
constantly excreted and evaporates; as "sweat" it is poured out in noticeable 
quantities, wetting the hair, or even running or dropping from the body. Sweat 
consists of water, 94.05 per cent; organic solids, 0.05 per cent; inorganic solids, 
5 per cent; with a specific gravity of 1020. StTbum; the secretion of the sebaceous 
glands is an oily substance produced by fatty metamorphosis of the cells of the 
gland; it is poured into the hair follicles, softens the hair and horny layers of the 
epidermis, keeping the skin soft, elastic and waterproof. 

The hoofs and horns are developed from the skin, and act as protective ap- 
pendages and weapons of defense. 

Milk. 

Is the secretion of the mammary glands (which are developed from the 
epidermis), is formed by the fatty" metamorphosis of the gland cells to supply the 
fat; the water, proteids, salts, etc., being secreted by ordinary cell action. Milk 
contains proteids, fat, sugar, salts, etc., in varying proportions, depending on the 
animal, its food, conditions of life, etc. 



CHAPTER XII. 

ANATOMY OF TILE EYE AND ITS APPENDAGES. 

The eye. 

Consists of a membranous sac containing certain transparent fluids or hu- 
mors of different densities. Placed in the orbit, resting on a cushion of fat, re- 
tained in position and directed toward the object in view, by a system of muscles. 

TiinJcs. 

The external tunic is the sclerotic, a fibrous membrane covering the posterior 
4-5 of the ball, and the cornea a transparent membrar?e covering the anterior 1-5. 
brane suspended in front of the lens; and the ciliary body uniting them. 

The inner tunic is the retina, the terminal expansion of the optic nerve. 

Humors. 

The aqueous humor occupies the space between the cornea and the iris, called 
the anterior chamber, and between the iris and lens, the posterior chamber, and 
certain recesses in the ciliary body. The vitreous humor occupies the posterior 
4-5 of the ball, the space between the lens and the retina. The lens is a bi-convex 
body suspended between the iris and the vitreous humor, attached to the ciliary 
body by the suspensory ligament. 

Appendages. 

The eye brows, rudimentary in the horse. The eye lids; upper and lower, are 
two movable curtains consisting of a central plate of cartilage covered externally 
by the skin, internally by the conjunctiva. In the anterior border a row of stiff 
hairs, the eye lashes, and small openings, the ducts of the Mebomian glands, 
which lie on the inner surface of the cartilage. The conjunctiva is a mucous 
membrane which lines the lids, covers the anterior portion of the ball and mem- 
brana nictitans and passes into the nasal duct. The membrana nictitans (or haw) 
consists of fibro-elastic cartilage covered anteriorly by conjunctiva, attached pos- 
teriorly to the fatty cushion, and is projected over the eye when it is retracted. 



82 VETERINARY ANATOMY, IHSTOLOGY, 



The lachrymal apparatus. 

Consists of the gland, caruncula, puncta, sac and duct. The gland is lodged 
between the orbital process of the frontal bone and the superior rectus muscle; 
its ducts opening on the inner surface of the upper lid. 

The caruncula lachrymalis is a small nodule near the inner canthus placed 
between the punctae, which are the minute openings of the lachrymal canals; 
these lead to the lachrymal sac, lodged in the fossa in the lachrymal bone, and 
communicating with the duct, a membranous canal lying in the conduit in the 
superior maxilla, and opening on the inner surface of the nostril above the in- 
ferior commisure. 

The ocular sheath. 

Is a dense fibrous membrane 1/ning the orbit, and enclosing its contents. 

Tlie capsule of Tenon. 

Is a serous membrane covering the eyeball from the sclero-corneal junction 
to the point of entrance of the optic nerve; where it is reflected over the tissues 
of the orbit as the parietal layer, passing forward to its point of origin. 

HISTOIX)GY OF THE EYE AND ITS APPENDAGES. 

Tlie eye. 

Is the organ of vision, consisting of the eyeball (bulbus oculi) and the optic 
nerve. 

Tunics. 

1. External; tunica externa (fibrosa) a continuation of tlie dura mater, con- 
sists Of an anterior transparent structure, the cornea, and the sclera. 

2. Middle; tunica vasculosa; the choroid, ciliary body and iris. 

3. Internal; tunica interna; an outer layer, the pigment membrane, and an 
inner, the retina. 

Humors. 

Are: The aqueous, vitreous and lens. 

Development . 

The eyes develop from the anterior brain vesicle, evaginations from which 
push forward toward the ectoderm, called primary optic vesicles, connected to the 
brain by slender processes, the optic stalks. An invagination of the anterior sur- 
face of the vesicle is now pushed inward forming a double walled cup, the second- 
ary optic vesicle or optic cup. A disc like thickening of the ectoderm sinks in- 
ward toward the cup, is later constricted off from the ectoderm forming the lens 
and its anterior epithelium. The outer layer of the optic cup becomes the pig- 
ment membrane; the inner layer becomes the retina. 

Sclera. 

Is a dense fibrous membrane perforated posteriorly for entrance of the optic 
nerve, forming the lamina cribrosa. Its fibers are placed in equatorial and meri- 
dional layers, the tendons of the straight muscles fuse with the latter, those of 
the oblique muscles with the former. The inner pigment layer is lined by endo- 
thelial cells which form the lamina fusca; the external layer by cells from the 
capsule of Tenon. The conjunctiva is united to the sclera by loose fibro-elastic 
tissue. The sclera and cornea unite by beveled edges; at the junction is an annu- 
lar venous sinus, the canal of Schlemm, which lies in a groove (inner scleral 
sulcus) in the anterior border of the sclera. 

Cornea. 

Consists of five layers: 

1. The anterior epithelium, layers of prickle cells, with lymph spaces. 



PHYSIOLOGY, COMPARATIVE ANATOMY 83 



2. Anterior elastic membrane (Bowman's) a homogeneous membrane pierced 
by nerve fibers which reach the epithelium. 

3. The ground substance, or substancia porpria, numerous lamellae of con- 
nective tissue cemented together and pierced by binding fibers (arcuate fibers). 
Between the lamellae are the corneal spaces containing leucocytes, corneal cor- 
puscles and lyinph. 

4. Descemet's membrane, or posterior elastic, which passes over to the liga- 
mentum pectinatum; this is a continuation of Descemet's membrane, encircles the 
anterior chamber, is attached to the anterior periphery of the iris, and is pierced 
by openings (spaces of Fontana) which communicate with the canal of Schlemm. 

5. The endothelium of Descemet's membrane is continued over the pectinate 
ligament and becomes the anterior endothlium of the iris. 

Choroid. 

Consists of four layers: 

1. External; lamina suprachoroidea, consisting of cells and lamellae of fibro- 
elastic tissue covered by endothelium; the spaces between the lamellae and be- 
tween this and the lamina fusca constitute the perichoroidal lymph spaces. 

2. Lamina vasculosa; an inner zone in horses and ruminants consists of con- 
nective tissue, the tapetum fibrosum; in carnivora, of cells, the tapetum cellulo- 
sum. An outer thicker zone consists of an inner layer of arteries, and an outer 
layer of veins, the latter converge toward four points on the ball at which they 
unite to form the venae vorticosae. 

3. Lamina choriocapillaris; contains no pigment, consists of capillaries which 
unite to form small radiating veins, the stellulae vasculosae. 

4. The glassy membrane; a very thin homogeneous membrane which extends 
forward over the ciliary body. 

The CUiary Body: 

Is that part of the choroid between the anterior border of the retina and 
the iris. Its posterior border is the orbiculus ciliaris; anterior to this it lies 
in folds, the ciliary processes, over which the glassy membrane extends. Internal 
to the glassy membrane is a double layer of epithelial cells, continued forward 
from the retina (pars ciliaris retinae), the inner layer clear, the outer pig- 
mented. In these cells are the ciliary glands which secrete the aqueous humor. 
Between the ciliary processes and the sclera, extending from the orbiculus ciliaries 
to the pectinate ligament is the ciliary muscle. 

The Iris: — Is a continuation forward of the choroid; forms a curtain in 
front of the lens, is attached at its anterior periphery to the pectinate ligament. 
It consists of three layers. 

1. The anterior endothelium, from Descemet's membrane. 

2. Thei stroma, or ground layer, consists of a thin anterior reticulate layer, 
and a posterior vascular layer, the bloodvessels having no muscle fibers, are in- 
closed in perivascular sheaths of connective tissue, 'as are also the nerves. In all 
eyes except in albinotics, this layer is pigmented. On the postero-internal border 
is a band of circular muscle fibers, the sphincter of the pupil; on the posterior 
surface a layer of radiate muscle fibers, the dilator of the pupil. 

3. The posterior epithelium is the double layer of the pars ciliaris retinae 
continued over the iris as the pars iridica retinae, both layers pigmented and con- 
tinuous at the margin of the pupil. 

Tlie tunica interna; nervous tunic. — Is composed of two layers. 
1. Is developed from the outer layer of the optic cup, consists of hexagonal 
cells containing black pigment granules, and having on their inner surface finger- 



84 VETERINARY ANATOMY, HISTOLOGY, 

like processes which project between the external segments of the layer of rods 
and cones. 

2. The retina; is developed! from the inner layer of the, optic cup; consists 
of a complex arrangement of nerve cells and fibers supported by a specially 
differentiated neurogliar tissue which pierces it from within outward in the form 
of long epithelial cells, called Muller's fibers, which expand at the ends into 
plate-like processes uniting at the edges to form the internal and external limit- 
ing membranes. 

The layers of the retina from without inward are: 

1. The layer of rods and cones, arranged in segments as follows: 

a. Outer segment of rod. 

b. Outer segment of cone. 

c. Inner segment of cone. 

d. Inner segment of rod. 

2. External limiting membrane, from Muller's fibers. 

3. Outer nuclear later. 

4. Outer molecular layer. 

5. Inner nuclear layer. 

6. Inner molecular layer. 

7. Ganglion cell layer. 

8. Layer of nerve fibers. 

9. Inner limiting layer, from Muller's fibers. 

The optic papilla is the point of entrance of the optic nerve; a depression in 
its center is the physiological depression. 

The macula lutea is a small yellow elevation in the visual axis, in its center 
a depression, the fovea centralis. There is no macula lutea in animals (Smith). 

The oi"a serrata is the notched anterior border of the retina. 

The optic iienre. 

Within the orbit the dura mater forms a sheath for the optic nerve and Is 
continued over the ball as the sclera. Internal to this is a sheath formed by the 
pia mater; between the two is a space divided by the arachnoid into two clefts; 
an inner continuous with the subarachnoid space, and an outer continuous with 
the subdural space. The fibers of the optic nerve have no neuralemma, are 
medullated, but loose this sheath as they pass through the tunics of the ball. 
Entering the ball at the lamina cribrosa they spread out to form the nerve fiber 
layer of the retina. 

Bloodvessels of the ttuiics. 

To the sclera, the anterior and posterior ciliary arteries, their capillaries enter 
the ciliary veins or the venae vorticosae. To the choroid; the posterior, anterior, 
and long ciliary arteries; the latter pass forward to the ciliary body, forming the 
circulus arteriosus iridis major. 

The anterior pass to the iris, break up into capillaries and form the circulus 
arteriosus minor at the inner margin of the iris. To the optic nerve and retina; 
the posterior ciliary arteries form the arterial circle of Zinn, around the optic 
nerve at the lamina cribrosa. The central artery and vein enter and leave at 
fhe optic papilla. 

Nerves of the tunics. 

To the cornea and sclera the ciliary nerves, which form several plexuses of 
sensory fibers in the cornea. 

To the choroid and iris; sympathetic neuraxes from cell bodies in the ciliary 
ganglia terminate in the ciliary and constrictor muscles of the iris; the cell 
bodies of these sympathetic neurones are surrounded by telodendria of medul- 



PHYSIOIX>GY, COMPARATIVE ANATOMY 85 

lated nerve fibers (white rami fibers) which reach the eye through the oculo 
motor nerves of the eye. Neuraxes of sympathetic neurones, the cell bodies of 
which are in the posterior cervical ganglia terminate in the radiating muscle 
fibers of the iris; these cell bodies are surrounded by the telodendria of white, 
rami fibers which leave the cord by the first, second and third thoracic nerves, 
reaching the superior cervical ganglia through the sympathetic. 
Humors of the eye, 

1. The vitreous is fluid with a small number of cells and leucocytes, sup- 
ported by thin structureless lamellae and fibers which coalesce at the periphery 
to form the hyaloid membrane which separates it from the retina. The hyaloid 
membrane passes over the ciliary processes, is attached to the ridges, leaving 
spaces which form a division of the posterior chamber inclosed by the hyaloid 
membrane, ciliary processes, the lens and its suspensory ligament, and are filled 
with aqueous humor. Passing through the vitreous humor from the optic papilla 
to the posterior surface of the lens is a transparent cord, in which there is 
neither lamellae nor fibers, called the hyaloid canal, is the remains of the anter- 
ior hyaloid artery of the fetal eye. 

2. Tlie lens. 

Is derived from the ectoderm in the form of a vesicle, the cells of the pos- 
terior wall become the lens fibers, the anterior wall remaining as the anterior 
epithelium of the lens. It is attached to the ciliary body by fibers rising from 
the pars ciliaris retinae, those rising from the free ends being attached to the 
posterior surface at the periphery; those rising between the processes to the an- 
terior periphery; between the two layers, surrounding the lens is a canal, the 
canal of Petit, which communicates by openings with the anterior chamber. The 
double layer of fibers forms the zonula of Zinn, or suspensory ligament of the 
lens. 

3. The aqueous humor; fills the anterior and posterior chambers, is secreted 
by the ciliary glands, is almost pure water, and is quickly renewed if removed. 

The lachrymal gland is a branched tubular gland, its ducts open on the 
mucous membrane of the upper lid; the watery secretion passes over the con- 
junctiva to the puncta, canals and duct. 

The Mebomian glands lie in the inner surface of the tarsal cartilage, their 
ducts opening on the margin of the lid, they resemble sebaceous glands. 

in, PHYSIOLOGY OF THE EYE AND ITS APPENDAGES. 

The eye is the organ of the special sense of sight; conditions necessary to 
vision are: 

1. A sensitive membrane, on which rays of light act as a stimulus, and by 
which the stimulus is transferred to the brain. 

2. A means of directing rays of light coming from different points to a focus 
at the same point. 

3. A means of directing rays coming from a near or far distance to a focus 
at the same point. 

4. A means of regulating the amount of light admitted to the membrane. 

5. Automatic control and harmony in action of all parts of organ. 

6. A means of directing the organ of vision toward any point. 

1. The I'etiiia. 

Rays reaching the retina pierce the inner layers to reach the rods and cones, 
this layer only being sensitive to light, and by which the stimulus is transferred 
to the brain. 

2. This is accomplished by the refracting media; the cornea and humors. 



»6 VETERINARY ANATOMY, HISTOIXJGY, 

Refraction. 

Rays falling perpendicularly on the cornea pass in a straight line to the 
retina. Rays coming from a distance greater than 20 feet are parallel, fall on 
the cornea in parallel lines, are refracted, and directed to a focus at the same 
point as the perpendicular ray. Rays coming from a distance less than 20 feet 
are divergent, fall on the cornea in divergent lines and are directed to a focus 
behind the retina; this gives a circle of diffusion at the retina, and produces a 
blurred image. 

3. This is accomplished by changes in the shape of the lens brought about 
by action of the ciliary muscle and the elastic fibers of the lens. "Accommoda- 
tion" is the term applied to this process. 

The normal eye, at rest, is focused to receive rays at the far distance (20 
feet or more), parallel rays from this distance meeting on the retina. The lens, 
which is elastic, is held partially compressed by the suspensory ligament attached 
to its circumference and to the ciliary body. 

The ciliary muscle originating from the scleral border, passes backward to be 
inserted to the outer surface of the ciliary body. The circle of diffusion falling 
on the retina generates an impulse which is reflected by the cilio-spinal center to 
the motor nerves of the ciliary muscle and sphincter of the pupil; these contract, 
the choroid is drawn forward, the suspensory ligament relaxed, the anterior sur- 
face of the lens bulges forward, becoming more convex, and the rays are directed 
to a focus on the retina with the perpendicular rays. The pupil contracts in 
order that rays passing through its circumference may be excluded; "rays passing 
through the circumference of a lens are more strongly refracted than rays passing 
through the center" this also gives a circle of diffusion on the retina, but is pre- 
vented by contraction of the pupil. 

Another change during accomodation is "convergence." Rays from the far 
distance being parallel, the visual axes of the eyes are parallel when at rest. 
Rays coming from the near distance being divergent, the axes must diverge pos- 
teriorly in order that the impulse may fall on corresponding areas of the retina. 
This is brought about by contraction of the internal recti, their motor nerves 
also being stimulated by the same impulse as the ciliary and sphincter. 

4. This is accomplished by the pupil, which reacts to various stimuli, the 
sphincter in accommodation for near objects, or by a strong light; the dilator 
by parallel rays or by a dim light. 

5. This is accomplished through the cilio-spinal center, its afferent and ef- 
ferent nerves; the stimulus of an imperfect image, or circle of diffusion on the 
retina is reflected by the cilio-spinal center to the efferent (motor) nerves. If 
cause is overstimulation of the retina by a bright light, the sphincter is contracted, 
if from insufficent light, it is dilated, etc. 

In accommodation the cause being an imperfect focus the impulse is re- 
flected to the ciliary, sphincter and internal recti muscles, the lens is changed, 
the pupil contracted, and the eyes converge. While the act of directing the eyes 
from a far to a near object is voluntary, accommodation is automatic. 

6. A means of directing the organ of vision toward any point desired. 

This is accomplished by the intrinsic muscles of the eye. Placed in the orbit, 
resting on a cushion of fatty substance, surrounded by a serous membrane lubri- 
cated by the fluid in the serous cavity of the capsule of Tenon, the eye represents 
a typical ball and socket joint. 

The voluntary muscles, taking origin from various points of the orbit, and 



PHYSIOLOGY, COMPARATIVE ANATOMY 87 

inserted at the periphery of the ball, exercise complete control of the organ. 
Holding it steadily at rest in any position, and changing the direction of the 
visual axes at will. At the same time certain movements of the eye are not 
under control of the will though the muscles are all voluntary muscles. The 
external recti cannot be stimulated by the will to cause divergence of the visual 
axes beyond parallel lines. 

One cannot be turned up or down, to the right or to the left, while the other 
is turned in the opposite direction; thus far the action of these voluntary muscles 
is automatic. 

For perfect vision the impulse must fall on corresponding areas of the retinae 
and only by having perfect harmony of action between the muscles of both eyes 
is this possible. 

Harmony between the voluntary and involuntary muscles is also necessary; 
if the eyes fail to converge for near objects accommodation is a failure also. If 
the pupil fails to dilate when the axes of vision are parallel for far vision, a suf- 
ficient number of parallel rays are not admitted, and vision is defective. This 
is also accomplished by the reflex action of the cilio-spinal center through the 
efferent nerves, as will be readily seen by a careful study of the anatomy and 
histology of this subject. 



CHAPTER XII. 
ANATOMY OF THE EAR. 

The organ of hearing consists of the external, middle, and internal ear. 

External. 

Consists of the conchal cartilage, or horn, which gives the ear its shape and 
receives the sound waves. 

The annular cartilage, attached to the bony canal, and around which the 
conchal cartilage is attached. 

The scutiform, an irregular plate acting as a lever between muscles and con- 
chal cartilage. 

These are covered by skin which passes into the external auditory meatus, 
forming the outer layer of the tympanic membrane. 

Middle. 

Consists of a cavity in the petrosal bone, bounded externally by the tympanic 
membrane, internally by the bony wall of the inner ear. Anterially the opening 
of the EHistacian tube, posteriorly the mastoid cells. Stretching across it from 
the tympanic membrane to the inner wall is a chain of small bones, the malleus, 
incus and stapes. It is lined by ciliated epithelium. 

Inner. 

Consists of a complex system of channels in the substance of the bone, 
within which is placed a like system of membranous channels. The bony chan- 
nels are, the vestibule, cochlea, and three semicircular canals. Within the vesti- 
bule are two membranous sacs, the utricle into which three semicircular mem- 
branous canals open, and the saccule into Which the cochlear tube opens. 



88 VETERINARY ANATOMY, HISTOLOGY, 

The internal auditoi-j' meatus is a small channel passing from the vestibule 
to the inner surface of the petrosal bone. 

The giittural pouch is a diverticulum of the Eustacian tube, and is found 
only in solipeds. 

The nerve to the ear is the eighth cranial. 

n, HISTOLOGY OF THE EAR. 
External. 

Is lined by skin; in that covering the annular cartilage are the ceruminous 
glands, modified sweat glands secreting a waxy substance. The tympanic mem- 
brane consists of three coats, outer of skin; middle of two layers of connective 
tissue, an outer of radiating, an inner of circular, fibers; thickened at the peri- 
phery to form the annulus fibrosus, which is attached to the periosteum at the 
sulcus tympanicus. The inner layer consists of mucous membrane covered by 
simple squamous epithelium. 

Middle. 

Consists of a cavity in the petrosal, separated from the inner ear by a bony 
wall in which is two openings; the fenestra ovalis closed by a membrane on 
which the stapes rests, and the fenestra rotundum closed by the inner tympanic 
membrane, on which the scala tympani of the inner ear rests. The Eustacian 
tube extends from the pharynx to the middle ear, opening into its anterior bor- 
der, having in its course a large diverticulum, the gutteral pouch, peculiar to 
solipeds. The mastoid cells open on the posterior border, are rudimentary in 
the horse. The malleus is attached to the tympanic membrane by its long process 
which is lodged between the layers of connective tissue; and to the bony wall 
by the processus gracilis. The head of the malleus articulates with the incus 
by a true joint and a meniscus; the short process of the incus is attached to the 
opposite wall, while its long process articulates with the stapes, also by a true 
joint; the stapes resting on the fenestra ovalis. The cavity is lined by ciliated 
epithelium, which extends into the Eustacian tube. 

Inner. 

Consists of a cavity, the vestibule, into which the cochlea and three semi- 
circular canals open. The semicircular canals are the superior, posterior and 
horizontal, each having near the vestibule an enlargement, the ampulla. They 
communicate with the vestibule by five openings; the contiguous limbs of the 
Superior and posterior uniting to form the canalis communis. The cochlea com- 
municates with the vestibule by the scala vestibuli. These constitute the bony laby- 
rinth within which is lodged the membranous labyrinth. 

The bony labyrinth is lined by endothelial cells. 

The cochlea consists of a spiral canal which winds around a central axis, the 
modiolus; a spiral plate of bone attached to the modiolus projects into the canal, 
called the lamina spiralis ossea; attached by one edge to this, and by the other to 
the outer wall of the canal is the lamina spiralis membranacea, the two dividing 
the canal into an upper channel the scala vestibuli which opens into the vesti- 
bule; and a lower, the scale tympani which) rests on the membrane closing the 
fenestra rotundum. These channels communicate at the last turn of the coch- 
lea by an opening, the helicotrema. 

The membranous labyrinth consists of the utricle, saccule, semicircular ca- 
nals, cochlear duct, an'd connecting tubes. 



PHYSIOLOGY, COMPARATIVE ANATOMY 89 

Uti'icle. 

Is a sac lying in the vestibule, opening into it three membranous semicircu- 
lar canals; and the scala vestibuli. The utriculosaccular duct connects it with 
the saccule. 

Saccule. 

Is a smaller sac also lying in the vestibule, connected to the cochlear duct by 
the canalis reuniens. 

Cochlear duct. 

Is a- closed tube lying in the cochlea above the lamina sprialis; resting on the 
floor of this tube is the organ of C'orti. 

The organ of Corti. 

Consists of neuro-epithelial cells resting on the floor of the cochlear duct; ar- 
ranged in an inner and outer row, the pillars or rods of Corti, which terminate 
in an expanded head or plate, those of the inner pillar overlying the outer, the 
arched space below is the arch of Corti, and the channel formed by the arches 
the tunnel of Corti. Leaning against the rows of pillars are the inner and outer 
auditory cells, terminating in an expanded zone from which rise a number of 
filaments, the auditory hairs. 

Neui'O-epithelial areas. 

In the utricle and saccule a macula; in the ampullae of the semicircular ca- 
nals the cristae, and in the cochlear duct the papilla spiralis (organ of Corti), 
from which rise hairlike filaments. 

Auditoi'y nerve. 

Enters the inner ear by the internal auditory meatus. Vestibular branche.s 
reach the macula of the utricle and the cristae of the superior and horizontal 
canals; a cochlear branch reaches the organ of Corti, and sends a branch to the 
macula of the saccule, and the crista of the posterior canal. 

The cochlear branch passes up [he modiolus, sending a sheet of nerve fibers 
into the bony lamina to reach the organ of Corti. Near the base of the bony 
lamina, along the entire length of the sheet of fibers, in a special canal, is a 
ganglion, the spiral ganglion of the cochlea. The neurones of this ganglion are 
bipolar, the dendrites pass through the bony lamina, under the rows of hair cells, 
and after losing the medullary sheath and neurilemma terminate in these cells. 
The neuraxes of these neurones pass down the central canal of the modiolus, and 
by the internal auditory meatus to the brain. 

Perilymph. 

Is secreted by cells lining the bony labyrinth, and fills the spaces between 
the bony and membranous channels. 

Endolyniph. 

Is secreted by the cells lining the membranous labyrinth, and fills all parts 
of it. 

ni. PHYSIOLOGY OF THE KAK. 

Sound. 

Is caused by vibrations; transmitted as waves the vibrations enter the exter- 
nal auditory meatus, set the tympanic membrane in motion, and are by it trans- 
mitted through the ossicles to the fluid of the internal ear. 

From the fenestra ovalis, the vibrations travel through the scala vestibuli, 
helicotrema, scala tympani, and as the membrane closing the fenestra ovalis 
vibrates inward, that closing the fenestra rotundum vibrates outward. 

During this process the vibrations are transmitted through the walls of the 
membranous labyrinth to the hair cells of the neuro-epithelial areas, by these 



90 VETERINARY ANATOMY, HISTOLOGY, 

conveyed to the nerve endings and conveyed by afferent nerve fibers to the brain. 

Eqiiilibiium. 

The function of the semicircular canals is to enable the animal to maintain 
a balance at all times; and is not concerned in the special sense of hearing, this 
being the special function of the organ of Corti. 

The impulses set up in the hair cells by movements of the endolymph in 
the canals, transmitted to the cerebellum, produce there impressions by which 
the animal is made conscious of the position of all parts of the body, and auto- 
matically executes the movements necessary to maintain a balance. 



CHAPTER XIV. 
00>IPARATIVE ANATOMY, 

The horse is taken as the standard for comparison. All differences are noted 
on this basis; a part being larger, smaller, more developed or less so; always con- 
sidered relatively. 

Tlie skeleton. 

I. OX. 

SkiilL Tlie fl'oiiCalj — Extends from below the eyes to the back of the 
skull; the frontal tuberosity forming the crest, also gives rise to the horn cores 
which rise from the supero-external angles; the supra-orbital foramina are double 
and placed far above the orbit; the frontal arch articulates with the zygoma. 

Parietal. — Narrow, elongated, placed under the horn cores, meets its fellow 
to form the inter-parietal suture beneath the crest posteriorly. 

Occipital. Smaller, wider transversely; neither crest nor tuberosities; con- 
dyles wider but less prominent; styloid processes shorter, broader, curved inward; 
condyloid foramina double or triple. 

Temporal. Squamosal and petrosal unite by ossification; the temporo-max- 
illary articulation; zygomatic, styloid, and mastoid processes are large. 

Sphenoid. The pterygoid foramen is absent; a large auditory bulla, and a 
large foramen ovale take the place of the foramen lacerum basis cranii; the 
foramen lacerum orbitale and rotundum form one. 

Ethmoid. Is well developed, a large volute forming a third turbinate bone. 

Nasal. Shorter, broader, the anterior extremity notched, making the nasal 
peak trifid. 

Superior maxilla. Shorter, broader, no spine, but a rough protuberance 
which does not join the zygoma; infraorbital foramen is opposite the first molar; 
there is no canine tooth. 

Premaxilla. Broad; no alveoli; no incisive foramen; incisive openings very 
large rarely unite by suture. 

Lachrynal. Large; forming at the bottom of the orbit a large protuberance. 

Malar. Large; bifid on posterior border, the upper branch meets the orbital 
process of the frontal; the lower, the zygomatic process of the temporal. 

Palatine. Large, broad; crest is thin and elevated, formed by the union of 
the palatine, pterygoid, and sphenoid bones; the pterygoid bones are large, placed 
between the sphenoid and palatine; the posterior nares are very narrow. 

Superior turbinal. Small; inferior, very large. 



PHYSIOIX)GY, OOaiPARATIVE ANATOMY 91 



Vomer. Large, resting on the anterior half of maxillary suture. 

Inferior maxilla. Longer, lighter, not united; eight incisor alveoli; condyles 
small, convex in the short, concave in the long, diameter; coronoid processes 
long, sigmoid notches very deep. 

Os hyoides. A cornu and two cornicula on each side; spur process small and 
blunt. 

"Vertebrae. Cervical, 7. Shorter; transverse process have an upper, small, and 
a lower large portion, pierced by the vertebral foramen; neural spines large, 
increase from before backward; inferior spines extend between the articular ends. 

Atlas. Smaller; no posterior lateral foramen; articulations wider. 

Axis. Is shorter; odontoid process broad; neural spine is not bifid, and 
does not reach the posterior articular processes; pedicles are perforated by a 
foramen. 

Sixth. Neural spine and transverse processes are long; no inferior spine. 

Seventh. Neural spine long, inclined backward; no inferior spine; no verte- 
bral foramen . 

Dorsal, 13. Bodies longer; foramina in pedicles in place of posterior notches; 
neural spines are broad, long, srhooth; first five or six incline backward, then 
upward; the remainder backward only. 

Lumbar, 6. Longer, thicker; transverse processes are long and broad, their 
anterior border concave, the posterior convex; the transverse processes do not 
articulate with the sacrum; or with each other. 

Sacrum. Larger, more arched, spines form a solid plate surmounted by a 
rugged lip; does not articulate with the transverse processes of the last lumbar; 
inferior surface more concave, promontory higher. 

Coccygeal. Fifteen to twenty; strong and tuberous; the anterior bones have 
articular processes. 

Ribs. Thirteen pairs; eight true, five false; straighter, broader, more uni- 
form; angles not well marked; distal extremities are expanded to articulate with 
their cartilages by true joints. 

Sternum, seven segments. A true joint between the first and second; the 
others uniting by ossification; cariniform cartilage is small and conical; the 
ensiform large and circular. 

Pelvis. Os Innoininatiini. Larger: 

Ilium. Thick, a prominent line from the anterior spine to the superior 
ischiatic ridge; ilio-pectineal eminence prominent; crest and spines very strong. 

Ischium. Large as the ilium; inferior spine conical, pointing outward and 
downward; a prominent ridge and tubercle on inferior surface of symphisis. 

Pubis. Large, concave, and never completely ossifies; acetabulum is deep; 
cotyloid notch deep and narrow; foramen ovale large. 

Pelvic Limb: 

Femur. Head small but prominent; trochanteric fossa small and deep; 
trochanter major has but one eminence; trochanter internus is a round tubercle 
near the posterior surface; no trochanter minor; condyles and trochlea small, 
supracondyloid fossa shallow. 

Tibia. No vertical fossa in anterior tuberosity; no facet for fibula; externa! 
malleolus detached, forming the malleolar bone. 

Patella. Small and conical. 

Tarsus, five bones. Astragalus is deep and narrow. Calcaneum long and 
square. Cuneiform magnum and cuboid united. Parvum very small. 



92 VETERINARY ANATOMY, HISTOLOGY, 

Large metatarsal. Divided at distal extremity by a deep fissure, small meta- 
tarsals rudimentary and single. 

Phalanges. Are double, each set forming a digit; they are small and nar- 
row, the OS pedis resembling one-half of that bone in the horse. 

Pectoral L/lnib: 

Scapula. Large, triangular; spine terminates by an acute angle prolonged to 
a point, the acromian process; neck more distinct; coracoid process and glenoid 
cavity small and close together. 

Humerus. Head large, tuberosities small; external trochanter very large, 
its summit curved over the bicipital groove, which is single. 

Radius. Short, having two radio-ulnar arches joined by a deep fissure. 

Ulna. Larger, extends to the distal end of radius, articulating with the cune- 
iform bone. 

Carpus. Six bones; upper row; scaphoid and lunar articulate with the radius; 
cuneiform articulates with the radius and ulna; and the trapezium, small and 
tuberous does not articulate with the radius. Lower row, os magnum and unci- 
form, articulate with the large metacarpal; the trapezoid and pisiform are wanting. 

Large metacarpal. Has a vertical groove in middle of anterior surface; 
inferior end divided by a groove into two articulations, each resembling the single 
one of the horse, the external one the smallest; a rudimentary metacarpus is 
placed postero-externally. 

Phalanges resembles those of the pelvic limb described above. 

Ossa cordis. Are two bones found related with the auriculo-ventricular rings 
of the heart of adult ruminants. 

Arthrology : 

Axial Skeleton: 

Supraspinous ligament is yellow elastic tissue; inferior common is very strong; 
intervertebral discs are thicker; ligamentum nuchae is stronger. True ribs ar- 
ticulate with their cartilages by true diarthroses having synovial membranes. The 
sternum has an inferior common ligament; the manubrium articulates with the 
mesosternum by a diarthrosis. Transverse lumbo-sacral and inter lumbar articu- 
lations are wanting. 

Arthrology. Pectoral Ldmb: 

The internal lateral ligament of the elbow joint is shorter than the external; 
the suspensory ligament divides into several parts; four of these go to the four 
sessamoids; the external pair give off a band which passes downward and for- 
ward, joining the tendon of the extensor proprius of the digit; two other bands 
rise from the ligament, pass through tlie central groove in- the metacarpus to 
join the same tendon from the inside; two small bands pass down to the claws 
and are continued to the postero-superior part of the distal phalanges; two deep 
branches go to the tendon of the flexor perfor&tus, forming two rings for the 
divided tendon of the perforans. 

The inferior sessamoidean ligaments are small, consisting of two lateral bands 
with a very small X ligament between them. 

The inter-sessamoidean ligaments are three; one joining each pair, and one 
joining the two internal bones. The superior inter-digital is crucial, joining 
the proximal phalanges; the inferior digital joins the distal phalanx and the 
navicular bone, and is attached to the perforans tendon. The superior navicular 
is of elastic tissue. 

Pelvic Limb: 

The pubio-femoral ligament is wanting in all animals except the horse. 



PHYSIOLOGY, COMPARATIVE ANATOMY 93 

There is but one straight patellar ligament in the smaller ruminants. 

The tarsus is more mobile in the ruminants, owing to the astragalus having 
more gliding motion. 

Myology. Head: — The pterygoid originates nearer to the median line, giving 
more lateral motion to the jaw; the digastric has but one belly, so is not a digastric 
muscle. The masseter and temporalis are smaller. The frontalis is a small muscle 
passing from the root of the horn core to the external levator of the eyelid. 
The levator labii superioris alaque nasi is not present in small ruminants; in the 
ox its anterior division covers the dilator naris lateralis and nasalis longus. The 
dilators of the nostril, except the lateralis, are v^^anting. The hyoideus magnus 
has a long tendon of origin, and no middle sheath, as there is no median digastric 
tendon. 

Tiiink: — The sterno-maxillaris is replaced by a band of the panniculus car- 
nosus, which is inserted to the masseter fascia; the sterno-sub-occipitalis is a 
muscle attached to the basi-occipital bone, with a tendon of the levator humeri. 
The sterno-thyro-hyoideus is larger and not digastric. The levator humeri is at- 
tached to the mastoid process, the posterior surface of the occipital, ligamentum 
nuchae, basi-occipital, and to the wing of the atlas by a separate tendon. 

The splenlus is very small. 

The trapezius and serratus magnus are very large. The intercostal and 
levators costarum correspond to the number of ribs. The pectoralis anticus is 
very small. The abdominal tunic is very large and thick; the lineae transversae 
very well marked. The obliquus internus is very large, filling the space be- 
tween the ilium, lumbar vertebrae and last rib. The diaphragm is large, the 
crura long and thick, and the periphery attached more anteriorly. 

Pectoral Liiiib: 

The extensor metacarpi obliquus is inserted to the metacarpi magnus. The 
extensor pedis is divided through its entire length, forming the extensor communis 
digitorum, and the extensor proprius internus; the tendon of the former divides, 
a branch being inserted to the pyramidal process of each distal phalanx; the 
tendon of the internus is inserted to the outer surface of the inner distal phalanx. 
The extensor suffraginis becomes the extensor proprius externus, inserted as the 
internus. The communis is an approximator, the proprii, divertors of the digit. 
The perforatus is double, forms a single tendon which later divides, each branch 
disposed as the single one in the horse, the ring being partly formed by the 
suspensory ligament. The perforans tendon divides, and is disposed as in the 
horse. 

Pelvic Limb: 

The gluteus externus blends with the triceps abductor; the magnus is smaller 
the internus larger. The tensor fasciae latae is large, and blends with the triceps 
abductor, which has no femoral attachment. The rectus parvus is wanting. The 
biceps rotator tibialis has no sacral origin. There is no pyriformis. The tendon of 
the obturator internus passes through the obturator foramen. The fibrous portion 
of the flexor metatarsi, and the extensor pedis have a common origin, giving rise 
to three large muscles; the external is the extensor communis digitorum; the 
inner is the extensor proprius internus, their tendons disposed as in the pectoral 
limb; the third is a flexor of the metatarsus, represents the fibrous portion of 
that muscle, forming a ring through which passes the tendon of the tibialis 
anticus, which represents the fleshy portion of the extensor metatarsi of the 
horse. The peroneus becomes the extensor porprius externus, and is disposed as 
in the fore limb. The peroneus longus lateralis is peculiar to the ox, originates at 



94 VETERINARY ANATOMY, HISTOLOGY, 

head of the tibia, and is inserted to the small cuneiform and metatarsal bones. 
The gastrocnemius is thicker; the flexor perforans more clearly divided into two 
parts. 

Digestive System: 

Lips. Of the ox are thick, rigid, nearly devoid of hair, covered by papillae 
and the orifices of subcutaneous glands which moisten it with their secretion, 
keeping it constantly moist in health. The lips of the smaller ruminants are 
thin, mobile and actively prehensile; the upper being divided by a median fissure. 

The cheeks. On the inner surface from the commisure to the first molar 
are covered by large conical papillae, a row extending backward along the level 
of the upper molars. 

Hard palate. Is large, the posterior third smooth, the anterior two-thirds 
covered by transverse, denticulated bars; behind the incisor pad is the openings of 
the canal of Jacobson. 

Soft palate is not so complete, the isthmus faucium being open. 

Tongue. Shorter, thicker, rougher, more pointed at the tip; is prehensile, 
with well developed muscles; the filiform papillae are very large and numerous 
near the point; the circumvallate are arranged in a row of ten on each side of 
the base. The tongue of the smaller ruminants is very delicate. 

Parotid gland. Small and red. The submaxillary large and yellow. 

The sublingual. Is in two portions, the posterior opening by a single duct 
(of Bartholini), the anterior by several. 

■^ Teeth. Neither canine nor incisor in the upper jaw. Eight incisors in the 
lower jaw. Molars are smaller, more cuboid. 

Pharynx. Large, its muscles blended. 

Oesophagus. Large, opening into the stomach by a funnel shaped dilatation; 
its muscle is red throughout, possesses both peristaltic, and anti-peristaltic action. 

Stomach. Consists of four compartments; the rumen, very large, occupies 
three-quarters of the abdomen; it is divided by fleshy pillars into right and left 
anterior sacs, and right and left conical sacs posteriorly; the division is incomplete. 
The internal mucous coat is cuticular, covered by leaflike, conical, and fungiform 
papillae. The rumen has two openings, both in the anterior aspect of the left 
sac; the upper is the oesophageal, and is continued over the lesser curvature of 
the second compartment by the oesophageal canal; the lower opening is large, 
entering the reticulum. 

The reticulum. The second compartment, the smallest of the four, is divided 
into cells giving it a honey-comb appearance; the mucous membrane is covered 
by papillae. It communicates with the left sac of the rumen, 'by a large opening; 
and with the omasum and oesophagus by the oesophageal canal. 

Omasum. The third compartment, consists of an outer envelope, filled by 
leaf like processes of mucous membrane: it has two openings; into the second and 
fourth compartments. 

Abomasum. Is the fourth, the true digestive stomach; its inner surface re- 
sembles the villous portion of the stomach of the horse. 

Small intestine. Is smaller caliber, but twice the length;. 

Ceacum. Is devoid of longitudinal bands; its blind end is blunt, and directed 
backward; it floats free in the abdomen. 

Colon. Is continuous with the end of the caecum, is arranged in coils, its 
length about thirty-six feet; its capacity is much less than the horse. 

Liver. Is very large, has a pear-shaped gall bladder, its duct entering the 
duodenum singly. 



PHYSIOLOGY, COMPARATIVE ANATOMY 95 

Pancreas. Differs little from the horse, its duct enters singly. 

Spleen. Is of same thickness throughout, with rounded extremities. 

Respiratoi'y System: 

Nostrils are narrow; nasal chambers communicate with the mouth by two 
openings near the incisor pad, the canals of Jacobson; the frontal sinuses are 
continued into the horn cores. The larynx is not well developed. The left 
lung has two lobes, the right has four, a third bronchus going to the extra lobe 
The thoracic cavity is smaller, the posterior mediastinum is imperforate. 

Urinary System : 

Kidney. Is lobulated in cortical portion; smooth in medullary. In shape Is 
elongated; the pelvis consists of a principal cavity, with a calyx for each lobule. 

Bladder. Larger, its peritoneal covering extending farther back. 

Genital System: 

Testicle. Well developed, long axis vertical globus major large; the vas 
deferens unites with its fellow at the neck of the bladder forming the common 
deferent canal, which opens into the urethra by two openings; the vesiculae 
seminales are large, lobulated, and glandular; their ducts entering the common 
deferent canal. 

Urethra. Diminishes in caliber from its origin; before the pubis it forms 
a double S shaped curve. 

Penis. Is long, thin, and projects far under the abdomen; anterior to the 
bulb it forms an S shaped curve, the inferior curvature forward. 

The glans is small, pointed, the urethra ending in a whiplike process of the 
corpus spongiosum. The sheath extends far forward; the prepuce is prolonged 
as an elastic sheath, which is furnished with four muscles, two protractors 
(anterior) and two retractors (posterior). 

The urethra is enveloped in the fibrous sheath of the corpus cavernosum, 
which is poorly developed. 

Ovaries. Are small. The uterus; fundus is short and narrow; the mucous 
membrane has a number of rounded vascular prominences, the maternal cotyle- 
dons. 

The labia of the vulva are thick, the inferior commisure narrow. • 

The udder consists of four mammae and four teats; in each quarter at the 
base of the teat is a large galactopherus sinus, from which an excretory canal 
proceeds down the center of the teat. In small ruminants there are two mammae 
and two teats. 

Circulatory System: 

Heart. Has two bones (see "skeleton"). There are twelve intercostals; the 
coeliac axis gives off on the left the artery of the reticulum, posterior to it the 
splenic, and farther back the hepatic; the terminal branch of the axis gives 
off the inferior artery of the omasum and abomasum. The anterior mesenteric 
artery divides into two branches; one to the small, one to the large intestines. 
The posterior mesenteric is small. The middle sacral is very large. 

The uterine artery is very large. 

The great metatarsal artery, with two veins, occupies the median groove or 
the anterior face of the bone; passing through the fissure in the distal end, 
reaching the back of the digit as the common digital, dividing into external and 
internal ungual, which pass down the inner aspect of the digits, entering the 
distal phalanx. 

The internal lateral digital is given off the great metatarsal; the external 
lateral digital is formed by the interosseous plantar and a transverse branch. 



96 VETEKEVARY ANATOMY, HISTOLOGY, 

The anterior aorta is wanting, or so short that the brachials may be said to 
rise from the common aorta. The dorsal and vetebral rise by a common trunk; 
the superior cervical is wanting; the vertebral does not inosculate with the 
occipital, but terminates in muscular branches. The humeral and most of its 
branches are small. 

The internal carotid is wanting, the occipital enters the cranium by the 
condyloid foramen; the lingual is given off the external carotid; the glosso-facial 
is found only in the larger ruminants. 

Nervous System: 

The cerebral convolutions are fewer but larger; the optic nerves are larger. 
The jugular ganglion and the pharyngeal branch of the tenth are very large. 
The recurrent nerves are separated from the vagus trunk by the breadth of the 
oesophagus. The spinal accessory divides into two branches. There are no 
other differences of any practical importance. 

The ox is taken as the standard for ruminants; the differences between 
this and the smaller ruminants will be here considered. All parts are compared 
with the ox as the standard, and relatively to the size of the animal. 

n. SHEEP AND GOAT. 

Skeleton, Frontal: — Is smaller and lighter; the frontal sinuses are not 
prolonged into the horn cores. 

Skull: 

Occipital. Forms the crest of the head, the superior curved lines occupying 
the summit, are very prominent. 

Sphenoid. The plate on the posterior border of the sella Turcica is high, 
curved forward, its angles prolonged, forming the posterior clinoid processes. 

Temporal. The mastoid process and crest are fused; the two portions unite 
late in life. 

Pre-maxilla. Is never articulated with the nasal by the summit of the ex- 
ternal process. 

Nasal. The spine is unifid as in the horse. 

Vertebrae, Cervical vertebrae. Are relatively longer than in the ox. 

Dorsal. Lighter; spinous processes not so wide; posterior notches are never 
converted into foramina. 

Lumbar. In the goat the transverse processes are inclined more downward; 
in the sheep more upward. 

Pectoral Lamb: 

Radius and ulna are longer. 

Pelvic Limb: — The pelvis is more horizontal and longer; the upper surface 
of the ischium and pubis less concave. 

Femur. The body is curved backward; the supra-condylold fossa nearly 
obliterated; the trochanter major level with the head; the inner and outer lips of 
the trochlea are equal in size. 

Tibia. Is longer than in the ox. 

Digestive System: 

Lips. Are thin, covered by hair, very mobile, and the upper is divided by 
a groove or fissure, which in the camel and sheep is complete, each half being 
moveable independant of the other. 

Tongue. Is not prehensile; is smooth and very delicate. 

Teeth. The incisors are narrow, neck very short, are more erect, more 
firmly fixed in the alveoli, and do not separate from each other in later life. 



PHYSIOLOGY, OOIMPARATIVE ANATOMY 97 

Urinary System: — The kidneys are not lobulated; the urethra is not en- 
veloped by the corpus cavernosum. The glans penis has two lateral folds at the 
base; the urethra is prolonged by a vermiform appendix, the extremity being a 
narrow cylinder, curved backward; the meatus is a longitudinal slit. 

in. HOG. 

Skull: — Ftontal is thick and short, the orbital process is short, the arch 
being completed by a ligament. 

Occipital. Forms a very prominent crest; condyles and foramen magnum 
small; styloid processes very long, inclining backward. 

Temporal. A single bone; petrous portion small, zygomatic process large; 
auditory meatus high up, styloid process short. 

Sphenoid. Short, pterygoid process large and flat. 

Nasal. Long, straight, strong; the peak projects nearly to the incisors. 

Lachrymal. Small; the fossa on the supero-external part, instead of in the 
orbit. 

Malar. Very strong; zygomatic process very large, terminating in two 
branches, between which rests the zygomatic process of the temporal. It does 
not unite with the orbital branch of the frontal. 

Superior maxilla. Short; surface concave; palatine foramen opens on the 
palatine plate of this bone. 

Pre-maxilla. Large, strong, not united at the symphisis; is no incisive 
foramen. 

Inferior inaxilla. Very strong; dental canal terminates in several mental 
foramina; seven molar alveoli. 

Vertebrae: — Cervical, seven. Very short; transverse processes bifid; anterior 
articular processes pierced by a foramen which enters the spinal canal. 

Atlas. Has a large tuberosity on upper surface. 

Axis. Small; transverse processes pierced by large foramina; neural spine 
is tall and thin. 

Seventh. Has large neural spine; transverse process pierced by a foramen. 

Dorsal, fourteen. Bodies short, increasing from before; neural spines broad 
decreasing from the first. 

Lumbar, six or seven. Bodies long; neural spines strong, pointed, bifid pos- 
teriorly, the diverging laminae reaching the posterior oblique processes. Trans- 
verse processes long, without articular processes. 

Sacrum, four segments. Neural spines rudimentary; laminae do not coalesce. 

Coccygeal, eighteen to twenty-three. The anterior ones have articular pro- 
cesses. 

Ribs. Fourteen pairs. Seven true, seven false; thin and flat. 

Sternum. Very long; seven segments. 

Pectoral LAnib: 

Scapula. Large, spine prominent, inclined backward. 

Humerus. Short; bicipital groove single; external trochanter very large. 
Radius. Small and much curved. 

Ulna. Is a true long bone, having a medullary canal; extends to the carput 
with which it articulates; does not unite with the radius. 

Carpus. Eight bones. Four in each row. 

Metacarpus, four bones. The middle pair are large, articulating with each 
other and with the external pair, which are small; all terminate as the single 



98 VETERINARY ANATO]\IY, HISTOLOGY, 

one of the horse, each digit having three phalanges, with sessamoid bones; the 
middle pair only reach the ground, and carry all the weight. 

Pelvis and Pelvic Liinib: 

The pelvis resembles that of the ox. The head of the femur is in front of 
the trochanter major; there is no trochanter minor. 

The fibula extends to the tarsus, articulating with the calcaneum. 

The tarsus is typical, except that the cuneiform medium is divided. 

The metatarsus resembles the metacarpals. 

Arthrology : 

The ligamentum nuchae is very rudimentary. There is but one synovial cap- 
sule in the occipito-atloid joint. There is a transverse ligament binding down 
the odontoid process. The ribs articulate distally like those of the ox. The 
suspensory ligament is replaced by the interosseous palmar muscles. There is 
no pubio-femoral ligament; and but one straight patellar ligament. 

Digestive System: 

The mouth is large; the upper lip fused with the snout; the lower short and 
pointed. Teeth; are the typical mammalian number. Twelve incisors, four canine, 
twelve pre-molars, sixteen molars. 

Stomach; is simple, the oesophagus opening into it by a funnel shaped 
dilatation, the cuticular membrane continued into it for two or three inches. 

The small intestines resemble those of the ox. The caecum resembles that 
of the horse in having longitudinal bands, but in shape is like that of the ox; 
directly continuous with the colon; thp latter is coiled as in ruminants. The 
liver is provided with a gall bladder, the biliary and pancreatic ducts entering 
singly. 

Respiratory System: 

The anterior nares are small round openings in the snout; it is always moist 
in health. The nasal fossae are long and narrow, the frontal sinuses extend back 
to the parietal bones. The larynx is loose and mobile, being attached to the 
heel process of the hyoid by the epiglottis. The epiglottis is very large; the lateral 
ventricles large and shallow. The trachea, bronchi, lungs and thoracic cavity 
resemble those of ruminants. 

Urinary System: 

Kidneys are large and simple as those of the horse; the ureters enter the 
bladder very near together. The bladder is large and projects into the abdominal 
cavity. The testicles are large and spherical; the vesiculae like those of rumi- 
nants. The penis resembles that of ruminants, but when flaccid is spirally 
twisted near the point; the sheath has no muscles. 

IV. CARNIVORA. 

The ovary is lobulated; the body of the uterus short, the cornua extremely 
long, resting among the intestines. The mammae are five or six on each side 
arranged in rows. 

CaiTiivora: 

Skull: — The frontal bones are triangular; the orbital process a peak; the arch 
jjompleted by a ligament; there is no supra-orbital foramen. 

Occipital. Very strong, terminating in a sharp pointed crest; styloid processes 
's'hort; the foramen lacerum basis cranii divided. 

Parietal. Very convex, meeting in a sharp ridge, continuous with the oc- 
cipital crest. The temporals are single, the zygomatic processes large and pro- 
jecting; hyoid process absent, and mastoid and styloid very small. Nasal; small. 



PHYSIOLOGY, COMPARATIVE ANATOMY 99 

wide in front with a concavity instead of a peak. Superior maxilla; short, strong, 
without spine. Six molar and one canine alveoli on each side. 

Pre-maxilla; short, incisive foramen small; six incisor alveoli. 

Inferior maxilla; strong-, rami broad, large; sigmoid notch vei-y deep; seven 
molar alveoli on each side; no interdental spaces; alveoli for two canine and six 
incisor teeth. Hyoid hone is triple, with two cornua and four cornicula. 

Vertebrae, Cervical, seven. The atlas has glenoid cavities posteriorly. The 
axis is long, the neural spine single, prominent, overlapping the atlo-axoid space, 
and may articulate with the atlas. The remaining segments decrease in size 
backward. 

Dorsal, thirteen. Neural spines strong; the first four or five equal, the rest 
decrease backward. Lumbar, six or seven. Neural spines incline forward, trans- 
verse processes incline downward and forward. Sacrum, three segments. Usually 
as broad behind as in front; neural spipe serrated, transverse processes bifid. 
Coccygeal, sixteen to twenty-one, the anterior resemble true vertebrae. Ribs, 
thirteen pairs, nine true, four false. 

Sternum, eight elongated cylindrical segments, which never unite. 

Pectoral Limb: 

Scapula; very large, spine central, terininating in the acromian process 
which curves backward near the glenoid cavity. 

Humerus; long, slender, curved but not twisted; external trochanter large, 
inner very small; bicipital groove single; coronoid and inter-condyloid fossae 
united by a canal. Radius and ulna equal in volume, articulate at the ex- 
tremities. The carpus, seven bones; four above, the scaphoid and lunar fused; 
three below. Metacarpal bones are five; four large and one small; the four 
large have each three phalanges and two sessamoids; the third sessamoid is re- 
placed by a ridge on the third phalanx; the small metacarpal has but two 
phalanges; between each metacarpal and its proximal phalanx there is a very 
small sessamoid anteriorly. 

Pelvis and Pelvic Limb: 

The pelvis is long, narrow, but very strong; the cotyloid cavity surrounded 
by a prominent border. The femur is long and straight, the supracondyloid fossa 
replaced by a tubercle; above each condyle a facet articulating with a sessamoid. 
The tibia and fibula are long, articulating at their extremities, and the fibula 
with the astragalus; there is a small sessamoid at the external head of the tibia 
The tarsus, seven bones; arranged as in the hog. Metatarsal, five, one of which 
is rudimentary; the four complete bones have each three phalanges, terminating 
as in the fore limb. There is usually a clavicle, incomplete in the dog, found 
imbedded in the soft structures between the sternum and shoulder. The os 
penis, a thin, elongated bone, hollowed for the urethra, both extremities pro- 
longed by cartilage. 

Muscular System: 

The panniculus carnosus is well developed; is continued over the haunch, and 
meets its fellow in the median line of the face and in the dorso-lumbar region. 
The orbicularis oris and buccinator are very rudimentary. The subcapulo- 
hyoideus is wanting; the sterno thyro-hyoideus rises from the first costal cartilage. 

Pectoral Limb: 

The antea and postea spinatus have each but one tendon of insertion. 

The extensor metacarpi magnus is inserted to the two inner metacarpal bones; 
the obliquus to the fifth. The extensor communis digitorum has four tendons, 
inserted to the three distal phalanges; the extensor proprius has three tendons in- 



100 VETERINARY ANATOMY, HISTOLOGY, 

serted to the three outer phalanges. 

The flexor perforatus has four tendons, inserted to the median phalanges of 
the four principal digits; the perforans has five tendons inserterd to the distal 
phalanges of all the digits. The ulnaris and radialis accessorius are present; the 
extensor pollicis et indicis rises with the obliquus and is inserted to the pollex 
and first digit. The antibrachial and rhetaearpal regions are furnished with 
muscles generally representing the human muscles of the same regions. 

Pelvis and Pelvic LAnib: 

The gluteus externus is very large; the maximus small, does not extend in 
front of the iliac crest, and is inserted by a single tendon. 

The triceps abductor femoris has no ischial origin; the sartorius originates 
from the venter of the ilium. The tibialis anticus rises from the tibial crest, 
and is inserted to the metatarsal bone of the pollex. The extensor communis 
digitorum rises from the fossa between the condyle and trochlea, and is in- 
serted by four tendons as in the anterior limb. 

The remaining muscles are disposed as in the anterior limb. 

Digestive System: 

Lips are not prehensile, but are thin and mobile; the upper has a median 
fissure. Tongue thin and very mobile; the sublingual gland is wanting. The 
dog has forty-two teeth; twelve incisors, four canine, twelve pre-molars and ten 
molars; four above and six below. They are entirely covered by enamel, and are 
of a brilliant whiteness. The cat has only fourteen molars, eight above and six 
below. 

The oesophagus is very dilatable, entering the stomach by an infundibulum; 
the stomach is simple, the mucous membrane villous. 

The intestines are short and small; the caecum is but a small spiral ap- 
pendix; the colon arranged as in inan, as an ascending, transverse, and descending 
part, without a floating colon. Near the anus, on each side, the rectum has the 
openings of two glandular pouches. The liver is large, the gall bladder on the 
middle lobe; the duct unites with that of the pancreas. The pancreas is 
elongated, and has two ducts, a small one unites with the hepatic, a large one 
enters the duodenum alone. The spleen is long and club shaped. 

Respiratory System: 

The septum nasi is prolonged, taking the place of the alar cartilages; the 
left lung has three lobes, the right four, the clefts between the lobes reaching 
almost to the root. The thoracic cavity is very large, the heart entirely surrounded 
by the lungs. 

Urinary System: 

The kidney is ovoid; the muscular coat of the bladder very strong. 

The testicles are placed in the perineal region below the anus. 

The vesiculae seminales are wanting, but the prostate gland is very large, 
forming a large bulb around the urethra (the knot). 

The penis is long, terminating in a point; the os penis is long and curved; 
its anterfor end fixed in the glans, its posterior attached to the corpus cavernosum, 
it has an inferior groove which lodges the urethra. 

There are no important differences in the female urino-genital organs. 



CONTENTS: 

Cliapter. Page 

I. The Skeleton . 3 

II. Articulations 10 

III. Muscular System 13 

IV. Vascular System 30 

V. Lymphatic System and Spleen 44 

VI. Nervous System . 48 

VII. Digestive System 59 

VIII. Respiratory System 66 

IX. Urinary System 70 

X. Generative System '''3 

XI. Skin and Appendages '''^ 

XII. Eye and Appendages 81 

XIII. Ear ^^ 

XIV. Comparative Anatomy 90 



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